Subject: Sci.chem FAQ - Part 6 of 7
Date: Sat, 18 Nov 1995 22:00:18 GMT
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Subject: 27. Fuel Chemistry

27.1  Where does crude oil come from?

The generally-accepted origin of crude oil is from plant life up to 3 
billion years ago, but predominantly from 100 to 600 million years ago [1]. 
"Dead vegetarian dino dinner" is more correct than "dead dinos".
The molecular structure of the hydrocarbons and other compounds present 
in fossil fuels can be linked to the leaf waxes and other plant molecules of 
marine and terrestrial plants believed to exist during that era. There are 
various biogenic marker chemicals such as isoprenoids from terpenes, 
porphyrins and aromatics from natural pigments, pristane and phytane from 
the hydrolysis of chlorophyll, and normal alkanes from waxes, whose size 
and shape can not be explained by known geological processes [2]. The 
presence of optical activity and the carbon isotopic ratios also indicate a 
biological origin [3]. There is another hypothesis that suggests crude oil 
is derived from methane from the earth's interior. The current main 
proponent of this abiotic theory is Thomas Gold, however abiotic and
extraterrestrial origins for fossil fuels were also considered at the turn 
of the century, and were discarded then. A large amount of additional
evidence for the biological origin of crude oil has accumulated, however
Professor Gold still actively promotes his theory worldwide, even though
it does not account for the location and composition of all crude oils.  

27.2  What are CNG/LPG/gasoline/kerosine/diesel? 

Crude oil consists mainly of hydrocarbons with carbon numbers between one and
forty. The petroleum refinery takes this product and refines it into several
fuel fractions that are optimised for their intended application. For spark
ignition engines, the very volatile and branched chain alkane hydrocarbons
have desirable combustion properties, and several fractions are produced.
          
CNG ( Compressed Natural Gas ) is usually around 70-90% methane with 10-20% 
ethane, 2-8% propanes, and decreasing quantities of the higher HCs up to 
pentane.  The major disadvantage of compressed gaseous fuels is the reduced 
range. Vehicles may have between one to three cylinders ( 25 MPa, 90-120 
litre capacity), and they usually represent about 50% of the gasoline range. 

LPG ( Liquified Petroleum Gas ) is predominantly propane with iso-butane
and n-butane. It has one major advantage over CNG, the tanks do not have
to be high pressure, and the fuel is stored as a liquid. The fuel offers   
most of the environmental benefits of CNG, including high octane. 
Approximately 20-25% more fuel than gasoline is required, unless the engine 
is optimised ( CR 12:1 ) for LPG, in which case there is no decrease in power 
or increase in fuel consumption [4,5].

Gasoline contains over 500 hydrocarbons that may have between 3 to 12 
carbons, and gasoline used to have a boiling range from 30C to 220C at 
atmospheric pressure. The boiling range is narrowing as the initial boiling 
point is increasing, and the final boiling point is decreasing, both 
changes are for environmental reasons. A detailed description of the 
composition of gasoline, along with the properties and compositions of CNG, 
LPG, and oxygenates can be found in the Gasoline FAQ, which is posted monthly 
to rec.autos.tech.

Kerosine is a hydrocarbon fraction that typically distils between 170-270C
(narrow cut kerosine, or Jet A1) or 100-250C ( wide cut kerosine, or JP-4 ). 
It contains around 20% of aromatics, however the aromatic content will be 
reduced for high quality lighting kerosines, as the aromatics reduce the 
smoke point. The major use for kerosines today is as aviation turbine (jet) 
fuels. Special properties are required for that application, including high 
flash point for safe refuelling ( 38C for Jet A1 ), low freezing point for
high altitude flying ( -47C for Jet A1 ), and good water separation 
characteristics.  Details can be found in any petroleum refining text and
Kirk Othmer.

Diesel is used in compression ignition engines, and is a hydrocarbon fraction 
that typically distils between 250-380C. Diesel engines use the Cetane 
(n-hexadecane) rating to assess ignition delay. Normal alkanes have a high 
cetane rating, ( nC16=100 ) whereas aromatics ( alpha methylnaphthalene = 0 ) 
and isoalkanes ( 2,2,4,4,6,8,8-hexamethylnonane = 15 ) have low ratings, 
which represent long ignition delays. Because of the size of the hydrocarbons,
the low temperature flow properties control the composition of diesel, and
additives are used to prevent filter blocking in cooler temperatures. There
are usually summer and winter grades. Environmental legislation is reducing
the amount of aromatics and sulfur permitted in diesel, and the emission of
small particulates ( diameters of <10um ) that are considered possibly
carcinogenic, and are known to cause other adverse health effects. Details 
can be found in any petroleum refining text and Kirk Othmer.

27.3  What are oxygenates?

Oxygenates are just preused hydrocarbons :-). They contain oxygen, which can 
not provide energy, but their structure provides a reasonable anti-knock 
value, thus they are good substitutes for aromatics, and they may also reduce
the smog-forming tendencies of the exhaust gases [6]. Most oxygenates used 
in gasolines are either alcohols ( Cx-O-H ) or ethers (Cx-O-Cy), and contain 
1 to 6 carbons. Alcohols have been used in gasolines since the 1930s, and
MTBE was first used in commercial gasolines in Italy in 1973, and was first
used in the US by ARCO in 1979. The relative advantages of aromatics and 
oxygenates as environmentally-friendly and low toxicity octane-enhancers are 
still being researched.

    Ethanol                                  C-C-O-H      C2H5OH
  
                                               C
                                               |
    Methyl tertiary butyl ether              C-C-O-C      C4H9OCH3
    (aka tertiary butyl methyl ether )         |
                                               C

They can be produced from fossil fuels eg methanol (MeOH), methyl tertiary 
butyl ether (MTBE), tertiary amyl methyl ether (TAME), or from biomass, eg 
ethanol(EtOH), ethyl tertiary butyl ether (ETBE)). MTBE is produced by 
reacting methanol ( from natural gas ) with isobutylene in the liquid phase 
over an acidic ion-exchange resin catalyst at 100C. The isobutylene was 
initially from refinery catalytic crackers or petrochemical olefin plants, 
but these days larger plants produce it from butanes.

Oxygenates have significantly different physical properties to hydrocarbons,
and the levels that can be added to gasolines are controlled by the EPA in
the US, with waivers being granted for some combinations. Initially the
oxygenates were added to hydrocarbon fractions that were slightly-modified
unleaded gasoline fractions, and these were commonly known as "oxygenated"
gasolines. In 1995, the hydrocarbon fraction was significantly modified, and
these gasolines are called "reformulated gasolines" ( RFGs ). The change to
reformulated gasoline requires oxygenates to provide octane, but also that 
the hydrocarbon composition of RFG must be significantly more modified than 
the existing oxygenated gasolines to reduce unsaturates, volatility, benzene,
and the reactivity of emissions.

Oxygenates that are added to gasoline function in two ways. Firstly they
have high blending octane, and so can replace high octane aromatics
in the fuel. These aromatics are responsible for disproportionate amounts
of CO and HC exhaust emissions. This is called the "aromatic substitution 
effect". Oxygenates also cause engines without sophisticated engine 
management systems to move to the lean side of stoichiometry, thus reducing 
emissions of CO ( 2% oxygen can reduce CO by 16% ) and HC ( 2% oxygen can 
reduce HC by 10%)[7]. However, on vehicles with engine management systems,
the fuel volume will be increased to bring the stoichiometry back to
the preferred optimum setting. Oxygen in the fuel can not contribute 
energy, consequently the fuel has less energy content. For the same
efficiency and power output, more fuel has to be burnt, and the slight
improvements in combustion efficiency that oxygenates provide on some 
engines usually do not completely compensate for the oxygen.
 
There are huge number of chemical mechanisms involved in the pre-flame 
reactions of gasoline combustion. Although both alkyl leads and oxygenates 
are effective at suppressing knock, the chemical modes through which they 
act are entirely different. MTBE works by retarding the progress of the low 
temperature or cool-flame reactions, consuming radical species, particularly 
OH radicals and producing isobutene. The isobutene in turn consumes 
additional OH radicals and produces unreactive, resonantly stabilised 
radicals such as allyl and methyl allyl, as well as stable species such as 
allene, which resist further oxidation [8,9]. 

27.4  What is petroleum ether?

Petroleum ether ( aka petroleum spirits ) is a narrow alkane hydrocarbon
distillate fraction from crude oil. The names "ether" and "spirit" refer
to the very volatile nature of the solvent, and petroleum ether does not
have the ether ( Cx-O-Cy ) linkage, but is just hydrocarbons. Petroleum
ethers are defined by their boiling range, and that is typically 20C.
Typical fractions are 20-40C, 40-60C, 60-80C, 80-100C, 100-120C etc. up
to 200C. There are specially refined grades that have any aromatic 
hydrocarbons removed, and there are specially named grades, eg pentane
fraction (30-40C), hexane fraction (60-80C, 67-70C). It is important to
note that most "hexane" fractions are mixtures of hydrocarbons, and pure
normal hexane is described as "n-hexane".  

27.5  What is naphtha?

Naphtha is a refined light distillate fraction, usually boiling below 250C,
but often with a fairly wide boiling range. Gasoline and kerosine are the 
most well-known, but there are a whole range of special-purpose hydrocarbon 
fractions that can be described as naphtha. The petroleum refining industry
calls the 0-100C fraction from the distillation of crude oil "light virgin
naphtha" and the 100-200C fraction " heavy virgin naphtha". The product
stream from the fluid catalytic cracker is often split into three fractions,
<105C = "light FCC naphtha", 105-160C = "intermediate FCC naphtha" and 
160-200C "heavy FCC naphtha".  

27.6  What are white spirits?

White spirits are petroleum fractions that boils between 150-220C. They can 
have aromatics contents between 0-100%, and Shell lists eight grades with 
aromatics contents below 50%, and six grades with aromatics contents above
50%. The two common "white spirits" are defined by British Standard 245, 
which states Type A should have aromatics content of less that 25% v/v and 
Type B should have an aromatics content of 25-50% v/v. The most common 
" white spirit" is type A, and it typically has an aromatics content of
20%, boils between 150-200C, and has an aniline point of 58C, and is 
sometimes known as Low Aromatic White Spirits. The next most common is 
Mineral Turpentine (aka High Aromatic White Spirits ), which typically has
an aromatics content of 50%, boils between 150-200C and has an aniline
point of 25C. For safety reasons, most White Spirits have Flash Points
above ambient, and usually above 35C. Note that "white gas" is not white 
spirits, but is a volatile gasoline fraction that has a flash point below 
OC, which is also known by several other names. Do not confuse the two 
when purchasing fuel for camping stoves and lamps, ensure you purchase the
correct fuel.   

27.7  What are biofuels? 

Biofuels are produced from biomass ( land and aquatic vegetation, animal
wastes, and photosynthetic organisms ), and are thus considered renewable
within relatively short timeframes. Examples of biofuels include wood,
dried animal dung, methyl esters from triglyercide oils, and methane from
landfills. The renewable aspect of most biofuels is essentially the use
of solar energy to grow crops that can be converted to energy. There is
a large monograph "Fuels from Biomass" in Kirk Othmer, and the subject
is frequently discussed in alt.energy.renewable, sci.energy, and 
sci.energy.hydrogen.  

27.8  How can I convert cooking oil into diesel fuel? 

Diesel engines can run on plant and animal triglycerides such as tallow
and seed oils, however most trials have resulted in reduced engine life, or
increased service costs. The solution is to transesterify the triglyeride
into esters, taking care to avoid the formation of monoacylglycerides
that will precipitate out at low temperatures or when diesel is encountered.
There are several plants in Austria that produce Rapeseed Oil Methyl Esters
as fuels for diesel engines. The economics of the process are very 
dependant on the price of diesel and the market for the glycerol byproduct.

The common catalysts used to transesterify triglyerides are sodium hydroxide,
sodium methoxide and potassium carbonate. If the esters are to be blended
with diesel fuel, then a two stage reaction is usually required to ensure 
monoacylglycerides are kept below 0.05%. Usually this involves using 22g of 
methanol ( containing 0.6g of sodium hydroxide ) and 100g of tallow 
refluxed for 30 minutes. The mixture is cooled, the glycerol layer removed,
and a further 0.2g of sodium hydroxide is reacted for 5 minutes at 35C in
a stirred reactor. The glycerol phase is allowed to separate, and the ester 
phase is washed with water to remove residual catalyst, glycerol and 
methanol. Note that sodium hydroxide is the most cost-effective catalyst,
but has the worst tendency to form soaps. The catalyst and methanol can
be industrial grade without further processing, however care should be
taken to prevent additional water entering the reaction. [10]. 

The fuel can be converted into other esters, such as ethyl and butyl, but
it really depends on the availability of cheap alcohol along with the
desired properties of the fuels. The New Zealand government investigated
a wide range of techniques for turning various vegetable and animal 
triglycerides into esters for diesel, and the reports cover many aspects 
of the kinetics and efficiencies [11]. There is a general overview of the
current processes and technology available in Inform [12]. A specific
techniques for analysing the monoglycerides has been published [13], however
I have found that acetylation followed by narrow bore ( 0.1mm ID ) capillary 
chromatography is faster and cheaper.  

------------------------------

Subject: 28. Pharmaceutical Chemistry

------------------------------

Subject: 29. Adhesive Chemistry 
   
------------------------------

Subject: 30. Polymer Chemistry 
     
30.1  How can I simply identify common plastics? 

Read the recycle code :-). Alternatively, give it to the nearest IR 
spectroscopist who has a polymer library. But if you want some fun, try the
following.
 
There are several simple tests that can be performed in the home that can
assist in separating common plastics, however it is important to realise that
formulated products contain large quantities of pigments, plasticisers, and
fillers that can dramatically alter the following properties. If possible
repeat the tests on a reference sample of the plastic.

a. Visually examine the sample, looking for recycle codes :-)
   While you are at it, you can check for indications of how the plastic
   was made - moulded, injected, rolled, machined etc. 
b. Try assessing the flexibility by bending, and look at the bending zone
   - does the material stretch or is it brittle? 
c. Test the hardness, try scratching it with pencils of differing hardness 
   ( B,HB,1-6H ) to ascertain which causes a scratch in the plastic. 
   Alternatively, attempt to scuff the sample with a fingernail. 
d. Cut a small slither with a sharp knife. Does the sample cut cleanly
   ( thermoplastic )?, or does it crumble ( thermosetting )?.
e. Hold sample in small flame, note whether it burns, self-extinguishes on
   removal from the flame, colour of the flame, and smell/acrid nature of 
   fumes when flame is blown out ( Caution - the fumes are likely to be 
   toxic ). Also attempt to press melted sample against a cold surface, and 
   pull away - does sample easily form long threads.    
f. Drop onto a hard surface, does the sample "ring" or "thud"?
g. Place it in water. Does it float, sink slowly, or sink rapidly?
   If it sinks rapidly, it is likely to be halogenated ( PVC, Viton, PTFE ) 
   If it sinks slowly, possibly nylon
   If it floats possibly poyethylene or polypropylene.
   - you can ascertain the actual density by adding measured volumes of  
     solvent until the sample neither rises nor sinks.

Cutting thin slivers results in powdery chips ( thermosetting )
 - carbolic smell in flame, self extinguishing = phenol formaldehyde
 - self extinguishing, black smoke, acrid = epoxide
 - fishy smell = urea formaldehyde, or melamine formaldehyde

cutting thin slivers results in smooth sliver ( thermoplastic )
 - metallic "ring", burns (styrene smell)  = polystyrene
   (note that high impact polystyrene may not give "ring" )
 - "thud", floats, hard, glossy surface, burns (paraffin wax smell) = 
      polypropylene
 - "thud", floats, medium-hard surface, burns (sealing wax smell) = 
      high density polyethylene 
 - "thud", floats, soft surface, burns (paraffin wax smell) =
      low density polyethylene 
 - "thud", sinks, burns ( fruity smell ) = acrylic
 - "thud", sinks, burns ( burning paper smell ) = cellulose acetate or
      propionate.
 - "thud", sinks, burns ( rancid butter smell ) = cellulose acetate butyrate
 - "thud", sinks, difficult to ignite ( greenish tinge ) = PVC
 - "thud", sinks, difficult to ignite ( yellow colour, formaldehyde smell )
      = polyacetal
 - "thud", sinks, difficult to ignite ( yellow colour, weak smell ), draws
      into long threads = Nylon
 - "thud", sinks, difficult to ignite ( minimal flame, decomposition but no
      charring, cellular structure forms = polycarbonate.
  
30.2  What do the plastics recycling codes mean?  

The recycle codes for plastics are currently being reviewed, and new codes
( probably inside a totally different symbol ) will soon be introduced.

1 = PET
2 = High density polyethylene
3 = Vinyl
4 = Low density polyethylene
5 = Polypropylene
6 = Polystyrene
7 = Others, including multilayer

------------------------------

Subject: 31. Others
     
31.1  How does remote sensing of chemical pollutants work? 

The are several techniques, but the one of most interest to the public is the 
system being used to identify grossly pollution vehicles. The system 
consists of an infra-red source on one side of the road, and a detector 
system on the other. The collimated beam of IR is directed at a gas filter 
radiometer equipped with two liquid-nitrogen-cooled indium antimide 
photovoltaic detectors. The beam is split and passes through 4.3um bandpass
filter isolates the CO2 spectral region, a 4.6um filter isolates the CO 
region, and a third filter isolates the HC region. A non-absorbing region 
is also used to compensate for signal strength. There are various specific
enhancements, such as the spinning gas-filter correlation cell in the 
University of Denver FEAT ( Fuel Efficiency Automobile Test ) system used
to cost-effectively identify grossly polluting vehicles [1]. "Optical remote 
sensing for air pollutants - review " by M.Simonds et al [2], provides a good 
introduction to the diverse range of instruments used for remote sensing of 
pollutants. 
 
31.2  How does a Lava Lamp work?

Contributed by: Jim Webb <jnw4347@email.unc.edu>

A container filled with clear or dyed liquid contains a non-water-soluble 
substance (the "lava") that's just a little bit denser (heavier), and has 
a greater thermal coefficient of expansion, than the liquid around it. 
Thus, it settles to the bottom of the container. A heat source at the 
bottom of the container warms the substance, making it expand and become 
less dense than the liquid around it. Thus, it rises. As it moves away 
from the heat source, it cools, contracts a bit, and becomes (once again) 
heavier than the medium. Thus, it falls. Heavy, light, heavy, light. 
Sounds like a Milan Kundera novel. 
(Actually, to be more precise: dense, less dense, dense, less dense.)

31.3 How do I make a Lava Lamp?

Contributed by: Jim Webb <jnw4347@email.unc.edu>

Method #1. A new, easy, simple, cheap lava lamp recipe

Use mineral oil as the lava. Use 90% isopropyl alcohol (which most 
drugstores can easily order) and 70% isopropyl alcohol (grocery-store 
rubbing alcohol) for the other ingredient. In 90% alcohol the mineral oil 
will sink to the bottom; slowly add the 70% alcohol (gently mixing all 
the while; take your time) until the oil seems lighter and is about to 
"jump" off the bottom. Use the two alcohols to adjust the responsiveness 
of the "lava." 

This mixture is placed in a closed container (the "lava lamp shape" is 
not required, although something fairly tall is good) and situated over a 
40-watt bulb. If the "lava" tends to collect at the top, try putting a 
dimmer on the bulb, or a fan at the top of the container.

To dye the lava, use an oil-based dye like artists' oil paints or a 
chopped-up sharpie marker. To dye the liquid around it, use food 
coloring. 

Two suggestions for better performance: 1) Agitation will tend to make 
the mineral oil form small bubbles unlike the large blobs we're all used 
to. The addition of a hydrophobic solvent to the mixture will help the 
lava coalesce. Turpentine and other paint solvents work well. To make 
sure what you use is hydrophobic, put some on your hand (if it's so toxic 
you can't put it on your hand, do you want to put it in a container that 
could break all over your room/desk/office?) and run a little water on 
it. If the water beads, it should work fine. 2) For faster warm-up time, 
add some antifreeze or (I've not tried it) liquid soap. Too much will 
cloud the alcohol. Keep in mind that the addition of these chemicals may 
necessitate your readjusting the 90% to 70% alcohol mixture.

Method #2. The official way. (from US Patent # 3,570,156 March 16, 1971)

The patent itself is not very specific as to proportions of ingredients. 
The solid component (i.e., the waxy-looking stuff that bubbles) is said 
to consist of "a mineral oil such as Ondina 17 (R.T.M.) with a light 
paraffin, carbon tetrachloride, a dye and paraffin wax." 

The medium this waxy stuff moves in is roughly 70/30% (by volume) water 
and a liquid which will raise the coefficient of cubic thermal expansion, 
and generally make the whole thing work better. The patent recommends 
propylene glycol for this; however, glycerol, ethylene glycol, and 
polyethylene glycol (aka PEG) are also mentioned as being sufficient.

This mixture is placed in a closed container (the "lava lamp shape" is 
not required, although something fairly tall is good) and situated over a 
40-watt bulb. If the "lava" tends to collect at the top, try putting a 
dimmer on the bulb, or a fan at the top of the container.

Method #3. The "less official" way (from Popular Electronics,[3] )How to make a
Lava Lamp, by Ralph Hubscher, 
  _Popular Electronics_ magazine, March 1991, p. 31 (4). Gernsback 
  Publications.)

Several non-water-soluble chemicals fall under the category of being 
"just a little bit heavier" than water, and are still viscous enough to 
form bubbles, not be terribly poisonous, and have a great enough 
coefficient of expansion. Among them: Benzyl alcohol (Specific Gravity 
1.043 g/cm3), Cinnamyl Alcohol (SG 1.04), Diethyl phthalate (SG 1.121) 
and Ethyl Salicylate (SG 1.13). [The specific gravity of distilled water 
is 1.000.]

Hubscher recommends using Benzyl Alcohol, which is used in the 
manufacture of perfume and (in one of its forms) as a food additive. It can 
be obtained from chemical or laboratory supply houses (check your yellow 
pages); the cheapest I could find it for was $25 for 500 ml (probably 2, 
maybe 3 regular-sized lava lamps' worth). An oil-soluble dye is nice to 
color the "lava"; Hubscher soaked the benzyl in a chopped up red felt-tip 
pen and said it worked great. [Benzyl alcohol is "relatively harmless", 
but don't drink it, and avoid touching & breathing it.] 

Hubscher found that the benzyl and the water alone didn't do much, so he 
raised the specific gravity of the water a little bit by adding table 
salt. A 4.8% salt solution (put 48 grams of salt in a container and fill 
it up to one liter with water) has a specific gravity of about 1.032, 
closer to benzyl's 1.043. I find that the salt tends to cloud the water a 
bit.. you might want to experiment with other additives. (Antifreeze? 
Vinegar?)

This is put into a closed container and placed above a 40-watt bulb, as 
above. Either way, I would suggest using distilled water and consider 
sterilizing the container by immersing it in boiling water for a few 
minutes.. algae growing in lava lamps is not very hip.

Caveat: Some of these chemicals are not good for you. Caveat 2: Some of 
these companies are not good for you if they find you've been infringing 
on their patent rights and trying to sell your new line of "magma 
lights." Be careful.

31.4  What is Goretex?

Goretex is a dispersion-polymerised PTFE that is patented by W.L.Gore and
Associates [4]. It is classed as a stretched semi-crystalline film, and is
produced by extrusion under stress ( faster take-up rate than extrusion 
rate ). The extrudate is stretched below the melting temperature, often
in the presence of an aromatic hydrocarbon that swells the amorphous region,
creating porosity. The hydrophobic nature of the PTFE means that liquid
water is repelled from the pores, whereas water vapour can pass through.
It is important to realise that once the PTFE pores are filled with liquid
water, the fabric can allow liquid water to pass though until it is dry
again. Thus Goretex-containing fabrics ( such as Nomex/Goretex - which 
consists of an outer aramid fabric, a central Goretex layer, and a cotton 
backing ) should never be used as protection from chemicals as many will
pass straight through. Any water-miscible solvent ( eg alcohol ) can fill 
the pores, and then liquid water can displace it and continue to rapidly 
pass through until the fabric is fully dried out.

31.5  What causes an automobile Airbag to inflate?

The final cause is the production of nitrogen from 10s of grams of sodium
azide, but there are some extra chemicals involved along the way.
Sodium azide is toxic, The airbag inflators are aluminum-encased units
that contain an igniter (squib), gas generant pellet or wafers of sodium
azide propellant and filters to screen out combustion products.
The electrical signal ignites a few milligrams of initiator pyrotechnic 
material. That then ignites several grams of booster material which then 
ignites 10s of  grams of sodium azide that burns to produce nitrogen gas
and sodium.  

The sodium azide is pelletized to control the rate of gas generation by
controlling its surface area. The free sodium would form sodium
hydroxide when it contacts  the water in people's noses, mouths, and
eyes so, to prevent this, the manufacturers mix in chemicals that will
produce sodium salts ( silicates, aluminates, borates ) on combustion.

Inflator units also often have a layer of matted material of alumina and
silica called Fiberfrax in the particulate filter. The Fiberfrax mat reacts
with most of the remaining free sodium in the generated gas.

There are apparently also corn starch and talcum powder used as lubricants 
in the bag, and if the bag explodes these are the powders that contaminate 
people - not the toxic chemicals in the inflator.  

One article quotes 160 grams  of propellant for a drivers-side bag 
( 60 liters of gas) and 450 grams for a passengers-side bags 
( which are 3-5 times larger) . I suspect that may include all of the
above ingredients in the igniter, but not the bag lubricants. 

Assume the bag reaches atmospheric pressure, the manufacturers
now control the bag inflation speed to 90-200mph, which is less than 
the early models - because they were too violent.
The sequence goes something like:-

0  - Impact
15 - 20 milliseconds - sensors signal severe frontal collision.
18 - 23 milliseconds - pyrotechnic squib fired
21 - 27 milliseconds -  nylon bag inflates
45 - 50 milliseconds - the driver ( who has moved forward 5 inches)
                       slams into the fully inflated bag
85 -100 milliseconds - the driver "rides the bag down" as the air
                       cushion deflates.

More details can be found in specialist articles [5-7], and research
is continuing into alternative inflation mechanisms, such as compressed 
gases. A major airbag supplier is Breed Automotive, Boonton Township, N.J.

31.6  How hazardous is the mercury from a broken thermometer?

First step - ensure the thermometer contained mercury, many sold for home
use contain alcohol. Mercury has an appreciable vapour pressure at ambient 
temperatures, thus if the mercury has split somewhere warm and with limited
air circulation, then concentrations can build up. When mercury drops any
distance it usually splatters into hundreds of small globules, resulting in
an increased surface area. The major hazard is mercury vapour produced from 
the spill. Mercury usually ends up in carpet or cracks in the floor, and so 
really is only a significant hazard to children crawling around the floor. 
Do not over-react, if the location is relatively cool and well-ventilated
there is little danger to adults - and if you read sci.chem you probably
already exhibit most of the symptoms of mercury poison. Remove as much 
mercury as conveniently possible, and just remember when toddlers come 
visiting that there is a slight potential hazard if the area is not 
well-ventilated and is warm. Obviously if you increase the ventilation, the
concentrations will decrease. The ACGIH TLV for mercury vapour is 0.05mg/m3,
whilst the DFG ( Germany ) is 0.01mg/m3, and the vapour pressure at 25C is 
0.0018mm. At 25C, the equilibrium concentration would be about 20mg/m3, 
which is 400 times the TLV. It is unlikely that this equilibrium would be
reached in areas where there are significant airflows unless the mercury
had been finely dispersed ( as in a blown manometer ).

Mercury vapour is rapidly oxidised to divalent ionic mercury by the tissues 
of the body. Human volunteers exposed to tracer doses of elemental Hg 
demonstrated first order kinetics for excretion with a half life of 60 days. 
The lethal concentration for humans is apparently not known, but acute 
mercurialism has resulted from exposures to concentrations within the range 
1.2 - 8.5mg/m3. The human organism is able to absorb and excrete substantial 
amounts of mercury, in some cases as high as 2 mg/day without exhibiting
any abnormal symptoms or physical signs [8].

The Dietary uptake for mercury was estimated to be :-
      3 micrograms/day Adults
      1    "        " young children
      1    "        "  infants.
and the adult uptake was estimated to comprise of
      0.3 air via Hg(0), 
      0.1 water via Hg(2+), 
      3 food via Hg(CH3Hg+).
( EPA Mercury Criteria Document 1979 )

The CRC Handbook of Laboratory Safety [9] has a chapter on mercury hazards.
A good discussion of mercury ( and other metals ) is found in "Metals and 
their Compounds in the Environment: Occurrence, Analysis and Biological 
Relevance" [10]. 

The best method of removing mercury is to use a vacuum with a flask and 
pasteur pipette and chase the little globules around the floor while not 
breathing :-).  Seriously, a simple vacuum system, or even a pasteur pipette, 
can remove most of the large globules. For nooks, crannies, and cracks where 
the mercury is likely to remain undisturbed, you can either apply flowers of 
sulfur ( fine elemental sulfur ) or zinc dust, with vigorous brushing to 
facilitate contact, and sweep up the excess. If the mercury is going to be
re-exposed ( by cleaning, foot traffic etc., ), then the zinc dust may be 
preferred because of an apparently faster reaction rate. However, if you 
have a light-coloured carpet, pouring yellow or grey powder is not usually 
an option, and if the location is warm and not well-ventilated near
ground level, ensure that toddlers do not spend hours every day playing there. 

There have been several studies, including "Vaporisation of Mercury spillage" 
[11]. The abstract says " A report on an investigation of the problem in
laboratories and industries of mercury ( Hg) vaporization from small droplets 
in cracks and floors. The efficacy of other fixing agents besides flowers of 
sulfur was metered. The results show that the use of a sulfur, calcium oxide 
and water mixture was the most successful mixture for fixing mercury droplets. 
A second convenient technique is the use of an aerosol hair spray. A 
chelating soap is available in some countries, and this would presumably be 
the method of choice in dealing with spillages."

One article includes methods based on amalgamating with zinc impregnated in 
a metal sponge or scrubbing pad for picking up mercury [12], and another
investigates substances that can be used to remove spilled mercury - such as
iodised activated carbon, copper or zinc powders, molecular sieves of copper 
or silver ions, and silica gel [13].

31.7  Did molasses really kill 21 people in Boston? 

From: mica@world.std.com (mitchell swartz) Date: Sun, 4 Jul 1993
Subject: Molasses Accident
 [excerpt from the Book of Lists #3 (Wallace et alia)]

  THE GREAT BOSTON MOLASSES FLOOD
  "On Jan. 15, 1919, the workers and residents of Boston's North End, mostly 
  Irish and Italian, were out enjoying the noontime sun of an unseasonably 
  warm day. Suddenly, with only a low rumble of warning, the huge cast-iron 
  tank of the Purity Distilling Company burst open and a great wave of raw 
  black molasses, two stories high, poured down Commercial Street and oozed 
  into the adjacent waterfront area. Neither pedestrians nor horse-drawn 
  wagons could outrun it. Two million gallons of molasses, originally 
  destined for rum, engulfed scores of persons - 21 men, women, and children 
  died of drowning or suffocation, while another 150 were injured. Buildings 
  crumbled, and an elevated train track collapsed. Those horses not
  completely swallowed up were so trapped in the goo they had to be shot by 
  the police. Sightseers who came to see the chaos couldn't help but walk in 
  the molasses. On their way home they spread the sticky substance throughout 
  the city. Boston smelled of molasses for a week, and the harbor ran brown 
  until summer."
   
  From this we see 21 people were killed, the half life was fairly short for 
  the contaminants. Long term effects were probably negligible.

31.8  What is the active ingredient in mothballs?

Mothballs were originally made from camphor  ( RN = 21368-68-3; MP = 176C; 
BP = 204C ) or naphthalene ( C10H8; RN = 91-20-3;  MP = 82C; BP = 218C ),
but para-dichlorobenzene ( C6H4Cl2; RN = 106-46-7; MP = 55C; BP = 173C )
became cheaply available as an unwanted byproduct of ortho-dichlorobenzene
production, and became the most common active ingredient. However, 
para-dichlorobenzene is also a suspected carcinogen, consequently the best
method of finding the active ingredient is to read the label on the packet,
as naphthalene has again become a common active ingredient. Note that adding 
mothballs to modern gasolines will not increase the octane - refer to the 
Gasoline FAQ posted in rec.autos.tech for more details.  

31.9  Is vinegar just acetic acid?

Most countries have food regulations that permit the use of acetic acid as 
clearly-labelled "synthetic white vinegar". Most vinegars are actually malt 
vinegars ( fermented ) and synthetic acetic acid is not allowed to be sold 
as Malt Vinegar. It can get rather messy when suppliers dilute malt vinegar
concentrates with acetic acid. Regulations usually require the addition
of acetic acid to be clearly marked on the label, and the product is not
normally legally sold as pure "malt vinegar".

31.10 What are the different grades of laboratory water? 

There are several techniques used in chemical laboratories to obtain the
required purity of water. There are several grading systems for water, but
the most well-known is the ASTM system, although certain applications (HPLC)
often require purer water than ASTM Type I, consequently additional
treatments such as Ultrafiltration and UV Oxidation may also be used to 
reduce concentrations of uncontrolled impurities, such as organics.

ASTM Type                                    I         II        III
Specific Conductance   (max. uMhos.)       <0.06      <1.0       <1.0
Specific Resistance    (min. Mohms.)      >16.67      >1.0       >1.0
Total Matter           ( max. mg/l )       <0.1       <0.1       <1.0
Silicate               ( max. mg/l )        N/D        N/D        0.01

KMnO4 Reduction        ( min. mins )      >60.0      >60.0      >10.0
Type                                         A          B          C
Colony Count           ( CFU/ml )        0 Bacteria   <10      <100 
pH                                          NA         NA       6.2-7.5 

The techniques to purify water are usually used in combination to obtain
high purity laboratory water.  

Distilled water is water that has been boiled in a still and the vapour 
condensed to obtained distilled water. While many impurities are removed 
( especially dissolved and undissolved inorganics that make water "hard", 
most organisms etc  ), some impurities do remain ( volatile and some 
non-volatile organics, dissolved gases, and trace quantities of fine 
particulates ). Distilled water has lost many of the ionic species that 
provided a pH buffer effect, so as it dissolves CO2 from the air during 
condensation and storage the pH moves to around 5.5 ( usually from close 
to neutral pH 7.0 ). 

Distilled water has the vast majority of impurities removed, but often those 
residual compounds make it unsuitable for applications, so there are 
other methods of purifying water to remove specific undesirable species, 
often these techniques use a lot less energy than distilling the water, and 
are used where large volumes of "pure" water are required. For smaller 
volumes, distillation is the pretreatment method of choice. 

The first treatment is usually a coarse physical filtration that can remove 
undissolved large particles. 

The next common treatment is  ion-exchange, which involves using a bed of 
resin that exchange with the dissolved species ( eg calcium, magnesium, 
chloride, sulphate ) that cause "hardness". Usually two resins are used, one 
that exchanges anions and one that exchanges cations, and the resins can be 
regenerated . These resins can be combined in a "mixed bed". If sodium 
chloride was present, the sodium ion would displace the hydrogen ion from 
the cation resin, while the chloride would displace the hydroxyl ion from 
the anion resin. The displaced ions will combine to form water. This 
technique produces "soft" process water that is often used in industry, and 
the water is described as "deionised".  If the water feeding the resin beds 
has already been distilled ( very common in laboratories - the resin beds 
then last much, much longer, and the distillation has also removed other 
impurities  ), then the water is called "distilled and deionised".
Laboratory water that has had most of the ionic impurities removed will have 
a high electrical resistance, and is often known as "18.3 megohm" water. 
( the electrical resistance is >18,300,000 ohm/cm ), but note that nonionic
impurities can still be present.    

An alternative process that has increasingly replaced ion-exchange is 
reverse-osmosis, which uses osmotic pressure across special membranes to 
remove most of the impurities. It is called reverse-osmosis because the 
feed side is pressurised to drive the purified water through the membrane 
in to opposite direction than would occur if both sides were the same 
pressure. The technique only removes 85-95% of ions, 99% of microbial 
material, and <99% of high MW organics. The huge advantage of RO is that 
membranes can easily be maintained ( occasional chemical sterilizations ), 
are largely self-cleaning, and can produce large amounts of water with 
minimal energy requirement ( just the pressure (200psi) to push the water 
along the membrane surfaces and improve the osmotic yield). RO is commonly 
used as a pretreatment stage when pure water is required, and for situations 
where large volumes of reasonably pure water are required. 
 
Organic species and free chlorine are usually removed from water 
by passing the water through a bed of activated carbon where they form
a low energy chemical link with the carbon. These filters are often 
installed upstream of the ion-exchange and reverse osmosis stages to protect 
them from the chlorine and organics in supply water.  

The final stage of producing "pure" laboratory water usually involves 
passing the deionised  water through a 0.22um filter, which is 
sufficiently small to remove the vast majority of organisms ( the smallest
known bacterium in around 0.3um ), thus sterilising the water. Recently,
Ultrafiltration has become popular as a means of reducing pyrogens ( they
are usually lipopolysaccharides from the degradation of gram negative 
bacteria ). The internal membrane has a pore size of <0.005um. This will
remove more particles, colloidal silica, and high MW organics such as
pyrogens. These filtration steps are usually applied at the point of use.
 
Ultraviolet irradiation can be used as a bactericide (254nm) or to destroy
organics by photooxidation (185nm). The water is exposed to UV for periods 
up to 30 minutes to destroy the organic material. 

Details of laboratory and industrial water-purification processes are 
available in the catalogues of equipment suppliers such as Barnstead [14]
and Millipore [15].  

31.11 What is Sarin nerve gas?.

Sarin is a nerve gas that was used in 1988 by Iraq against its Kurdish 
population, and in 1995 by Japanese terrorists against Tokyo subway users.
Sarin and its companion nerve gases ( Tabun and Soman ) were discovered 
in the late 1930s by Gerhard Schrader at I.G.Farben during research into 
pesticides. The lethal dose for humans may be as low as 0.01mg/kg [16], 
unless treated immediately. Sarin inhibits with acetylcholinesterase, an 
enzyme that breaks down acetylcholine. Acetylcholine carries signals between 
nerves and muscles, and buildup causes overstimulation of muscles ( including 
the involuntary ones controlling  eye, lungs, bowel ), which then go into 
spasms. Treament involves atropine ( shuts down the overstimulated nerves ), 
or oxime drugs ( can prise Sarin off the enzyme ), and must be immediate.  
More details and references can be found in the Merck Index.

There are many different methods of manufacture, but the Tokyo product
appears to have been prepared using a procedure involving phophorus 
trichloride and methyl iodide. The product was impure and diluted with 
acetonitrile to improve volatility. To stockpile Sarin, the product has to 
be pure ( 90-99% of the Iraqi Sarin degraded in < 2 years, whereas US Sarin 
only degraded a few % over 30 years ). The standard US goverment procedure 
( aka "di-di" ) starts with dimethyl methylphosphonate (DMMP), and ends
with a distillation to remove impurities [17].

    O                  O            O                  O     CH3
    ||     thionyl     ||   HF      ||  isopropyl      ||   /
CH3-P-OCH3 ------> CH3-P-Cl --> CH3-P-F ---------> CH3-P-O-CH   
    |     chloride     |            |    alcohol       |    \
    OCH3               Cl           F                  F     CH3

   DMPP              Dichlor     Difluor            Sarin (GB)


31.12 What are Dioxins?

"Dioxins" are a group of closely-related compounds which are known as
polychlorinated dibenzo-p-dioxins (PCDDs). "dioxins" also commonly includes 
polychlorinated dibenzofurans (PCDFs). All organic molecules that contain 
chlorine are also members of the "organochlorine" family.

               1       9                    1       9
             2/ \ _o_ / \8                2/ \ ___ / \8  
             | O |_o_| O |                | O |_o_| O |
             3\ /     \ /7                3\ /     \ /7
               4       6                    4       6

            Dibenzo-p-dioxin              Dibenzofuran

As dioxins are fat soluble, they will accumulate in fatty tissue. In general, 
it is only the biologically active ( molecules containing the 2,3,7,8 
substitution ) congeners that accumulate, with levels of the higher 
homologues predominating [18]. It is important to remember that of all the 
dioxins and furans, only those containing 4 to 8 chlorine atoms, _and_ with 
chlorine atoms in the 2,3,7,8 positions are currently considered toxic. 
The compounds only containing 0 to 3 chlorine atoms are currently not 
considered toxic, however once all four of the 2,3,7,8 positions are filled, 
the most toxic congener is created ( 2,3,7,8 TCDD = "dioxin" ). As additional 
chlorines are added, the toxicity decreases, except that 2,3,4,7,8 
pentachlorodibenzofuran is more toxic than 2,3,7,8 tetrachlorodibenzofuran.

There is evidence that suggests concentrations of dioxins and furans in 
human adipose tissue are falling [19]. The analysis for dioxin can reliably 
detect ppq ( parts per quadrillion = picograms/kilogram ) levels, but some
evidence suggests dioxins may still have toxic effects at such low levels. 
The toxicity of dioxins is currently being carefully assessed by the US EPA 
- who are due to present a comprehensive report in the next few months. The 
draft of the report, and various reviews, have been available for public 
comment and external peer review. A good discussion of current perceptions
is available in a special report published in the January 1995 Environmental 
Science and Technology [20], where both sides of the debate are presented. 
Dioxins can arise naturally from forest fires, but the major sources are
from incineration and the manufacture and use of organic chemicals. Most
other sources involve combustion ( leaded gasoline, coal combustion, 
metallurgical processes )[18].   

As the various congeners have differing toxicity, dioxins are usually 
reported using Toxic Equivalents systems. These assign to each congener a 
toxicity factor relative to 2,3,7,8-TCDD, and these factors are used to 
calculate the 2,3,7,8-TCDD Toxic Equivalent. The International Toxic
Equivalent Factor (I-TEF) system, proposed by the Challenges to Modern 
Society Committee of the North Atlantic Treaty Organisation is widely used.  
  
Food is the major source of dioxins for humans, and typical dietary intakes 
in the US for a 65kg adult were estimated to be between 18-192 pgTEQ/day [21],
and UK intakes were estimated to be 125 pgTEQ/day [18]. The Regional Office 
for Europe of the World Health Organisation suggests 10 pg/kg body weight/day
for 2,3,7,8-TCDD ( 600 pgTEQ/day for 60kg person ), as a Tolerable Daily 
Intake, whereas the US-EPA suggests an intake of 0.006 pg/kg/day over a 70 
year life will lead to one excess cancer in one million people. 
Sources of Dioxins in the UK diet                  pgTEQ/day
Meat, meat products, poultry, and offals            38
Cow's milk                                          23 
Fats and oils                                       19
Milk products                                       12
Fish                                                 7.7
Eggs, cereal products, fruit, and vegetables        25.3

31.13 What is Red Mercury?

Red mercury is supposed to be a very powerful explosive that is being made 
in Russian nuclear reactors. According to one report, it is a cherry red and 
semi-liquid compound of pure mercury and mercury antimony oxide that is 
irradiated for up to 20 days in a nuclear reactor [22]. It is claimed that 
when incorporated in a fusion bomb, it can yield sufficient chemical energy 
to fuse tritium atoms. Experts are skeptical that such an energetic compound 
could be sufficiently stable to be used as an explosive.  

31.14 How do I remove stains and deposits?

- Test any planned treatment on an unimportant part of the material first,
  (spots and holes aren't currently fashionable ).
- Chemicals for removing stains are often toxic and corrosive, handle with
  care, and follow any provided safety instructions.
- Often stains are a diverse mix of chemicals, and the best solution is
  to solubilise as much as possible, remove imsoluble material through
  washing, and then carefully bleach. Chemists should not assume they can
  perform this process better than housewives. 
- Some stains are more easily removed by physical means - such as using
  abrasives ( household cleaning pastes, steel wool, metal polishes, etc ),
  or freezing solid and scraping ( chewing gum ).
- The fresher the stain, the easier to remove. Avoid using hot water or soap 
  on unknown stains, and use solvents (eg glycerine) to help keep the stain
  fresh. In cases when the stain is known to be water-soluble (eg bird 
  droppings ), it is often preferable to allow the stain to dry and carefully 
  scrape most away, before additional treatment.
- When using solvents, apply around the outer edge of the stain and work 
  towards the centre to prevent a stain ring forming. 
- Many stains result from pigments, and they are seldom soluble, so once the
  other components are removed, use physical agitation to remove the 
  insoluble material.

There are books on stain removal [23,24], and many of the common recipes are 
also often found in some homecare and cookery books. Most homecare magazines 
also have question and answer sections that frequently include advice on 
how to remove specific stains. Very few chemical books cover chemical 
cleaning and stain removal, and smart chemists avoid offering to remove 
stains :-). Common stains are usually attacked with the household chemical 
arsenal that may include:-
* Absorbents - Cornflour, french chalk, fuller's earth, starch, talcum powder.
* Acids - Inorganic = hydrochloric ( galvanising remover, concrete cleaner ). 
        - Organic = acetic ( white vinegar ), citric ( lemon juice ), 
                    tartaric ( cream of tartar ) 
* Alkalis - Sodium hydroxide ( drain cleaner ), ammonia solution, 
* Bleaches - Sodium hypochlorite solution ( household bleach ), calcium 
             hypochlorite ( bleaching powder ), hydrogen peroxide 
* Drycleaning Fluids - 1,1,1-trichloroethane, perchloroethylene.
* Enzymes - Pepsin
* Petroleum Fractions - mineral turpentine, kerosine, gasoline, white spirits.
* Sodium carbonate ( washing soda ), sodium bicarbonate ( baking soda ),
  sodium tetraborate ( borax ).
* Solvents - Acetone ( nail polish remover ), amyl acetate, methanol, ethanol 
             ( methylated spirits ), glycerine, toluene, xylenes, iso propyl 
             alcohol.
* Terpenes - Eucalyptus oil, citrus oil, camphor 

Specific Stain Strategies.
Ballpoint - methylated spirits, fullers earth, glycerine.
Blood - cold salty water, cornflour paste, or dilute bleach.
Copper deposits on sink or bathtub - ammonia (1 hr) then detergent.
Chewing Gum - freeze, or sponge with eucalyptus oil.
Chocolate - methylated spirits, or soak in 5% borax solution
Lipstick - glycerine, eucalyptus oil, drycleaning fluids.
Rust - oxalic acid, citric acid, tartaric acid
Tar - toluene, xylenes, eucalyptus oil.
Tea or Coffee - glycerine, warm borax solution
Wine - glycerine, borax solution, lemon juice

31.15 How do I remove rust? 

It depends on the sample and amount of rust. If the material is heavily 
rusted, then physical techniques ( sand blasting ) may be appropriate. 
Chemical techniques on steel usually involve phosphoric acid, and the 
concentration depends whether the treatment can be washed off. An 
excellent discussion is available in  Product Finishing [25], along with
simple formulations. For removing light rust without subsequent removal
of the solution, 15% H3PO4 + 4% nC4OH + <0.1% H2SO4 is used, but if the
solution can be washed away, then 33% H3PO4 + 2% nC4OH is preferred.

31.16 How do I electroplate or anodise materials?.

There are several excellent books and journals on metal treatments in the
hobbies and metalworking sections of public libraries. For the serious
plater, the journals Surface Finishing and Product Finishing discuss all the
the chemical and electrical aspects - including disposal and destruction of
wastes. Their Annual Handbooks, along with the Canning Handbook of
Electroplating, have many recipes and details for the serious electroplater.
In any metal finishing process the preparation of the substrate is of
great importance, and the recommended sequence of cleaning, pickling,
plating, and especially passivating should be carefully followed. 
Failure to correctly passivate newly deposited protective surfaces is the
main cause of the rapid formation of unsightly corrosion products. 
There are specialist books for the metalworking hobbyist that only wants 
to occasionally plate items, and some should be available in public
libraries.

31.17 How fast do solvents pass through human skin?

It obvioulsy depends on the solvents, and traditional measurements have
been made using dead skin, but some recent work has provided a simple
comparison of individual solvents. It must be emphasised that mixtures of
solvents have significantly different rates [26]. 

 Permeability Constants in g/m2h 
 Solvent                        Average          Standard Deviation
 Dimethylsulfoxide                176                   42
 N-Methyl-2-pyrrolidone           171                   59
 Dimethylacetimide                107                   19
 Dimethylformamide                 98                    1.1
 Methyl ethyl ketone               53                   29
 Methylene chloride                24                    8.4
 Water  [^3H radiolabeled]         14.8                  0.1
 Ethanol                           11.3                  0.5
 Butyl acetate                      1.6                  0.1
 gamma butyrolactone                1.1                  0.1
 Toluene                            0.8                  0.7
 Propylene carbonate                0.7                  0.4
 Sulfolane                          0.2
  
------------------------------



