James said " but the
 reaction of the anhydride with the air can be described
 equally well as
 either "hydrolysis" or "oxidation"."

I am sorry but this is simply incorrect.  Chem 101 defines oxidation as a chemical reaction which involves a change in valence state.  Butyric anhydride does not react at all with oxygen at room temperature and when it reacts with water there is no change in valence state.  Calling this reaction an oxidation is simply incorrect.  It is a hydrolysis which is defined as the chemical addition of water to some molecule.  Hydrolysis and oxidation are two entirely different chemical processes with nothing in common. There is an easy way to tell butyric anhydride does not react with oxygen at room temperature.  Just open a half bottle that has been stored a while.  When you loosened the can did the bottle suck air in?  Nope.  Yet the head space in that bottle was 20% oxygen.

James said " As far as I know,
 very low humidity has never made
 butyric anhydride less effective or less stinky. "

This is simply an irrelevant red herring.  The odor of butric anhydride is not expected to be the same as the odor of butric acid.  They are two entirely different chemicals with each having its own odor.

James said " Volatile organic compounds are also produced by the reaction
 (the very foul
 odor). The proof is that butyric acid is far less
 foul-smelling than the
 anhydride, despite the much lower vapor pressure of the
 anhydride, which
 (for most substances) would tend to reduce the
 "evaporation", and hence the
 fume level"

The only product of hydrolysis of butyric anhydride is butyric acic.  The type of odor has very little to do with vapor pressure.  Odor can even change with changes in your genetics and changes in concentration.  Some things smell good when in low concentrations to some people and terrible in higher concentrations.  Pyridine for example.  So the statement that a different smell proves anything is simply wrong.  At room temperature butyric anhydride does not react at all with oxygen.  It will burn at high temperatures and this is an oxidation reaction with oxygen in the air.  During burning all sorts of volatile organics can be produced during incomplete combustion and some will have health consequences if inhaled.  This is no different from using wood in your smoker.  I use ash personally but have also used maple.  I have not had the slightest problem with that wood oxidizing at room temperature.  If burned in excess oxygen at high temps it does not produce smoke.  At lower temperatures and with a deficiency of oxygen it produces clouds of smoke.  I suggest bee keepers try to avoid breathing the smoke as much as possible.  Smoke in your lungs is not good for you.  It is a good bet that smoke from combustion of any organic, including wood, will contain carcinogens.

James said " The word "CORROSIVE" is featured in very large bold print on
 every MSDS for
 the chemical.
 It is a class 8 Corrosive Liquid under CFR 49 Section 172
 (the shipping
 regulations).
 If one gets some in one's eye or on one's skin, one will
 find out exactly
 how corrosive.  "

This is just a repetition of what I said.  Exposure to either by way of skin, lungs or eyes can cause a chemical burn.  How severe the burn is depends on concentration of exposure and how long before the substance is flushed from the skin in case of a spill on your hands for instance.  Spill either the acid or anhydride on your hands and immediately wash it off and you will get no burn at all.  It is a bit more difficult to wash your eyes rapidly and impossible to wash your lungs.  Any chemical which will cause a burn under any conditions is going to be labeled corrosive.  That probably includes vinegar. I looked up the MSDS for acetic acid, which is the active chemical in vinegar, and it is rightly labeled as a corrosive. It is a rather sweeping term in broadness and by itself tells you very little other than the potential for harm exists if used improperly.  Just because something is labeled corrosive does not tell you anything about what it is corrosive to, nor how severe that corrosion might be in terms of tissue damage.  A big problem with MSDS statements is they are aimed at the general public and stated to provide the maximum warning.  People like fire fighters want to see MSDS statements to protect themselves.  So, catch all words like corrosive are used to warn against any exposure at all.  As I said prior the ideal exposure is always zero.  That is what a fire fighter wants.  They go into situations in haz mat suits and Scott Air packs so they can be reasonably sure they have zero exposure.  Chemists operate in fume hoods for the same reason.  This does not mean small exposures are a problem in all cases.  People routinely put acetic acid vinegar on their salads and eat it and think it tastes good and is healthy.  The State of CA requires a label on play box sand stating that it is a known carcinogen to the State of CA.  Can your kid get cancer from playing in play box sand?  Of course not.  However, take that sand and grind it down to 1 micron or smaller and inhale enough of it and you get silicosis of your lungs and that can evolve into cancer.  CA simply takes an extreme experiment and generalizes it to all forms of silicon dioxide which is chemically what sand is.


Dick

" Any discovery made by the human mind can be explained in its essentials to the curious learner."  Professor Benjamin Schumacher talking about teaching quantum mechanics to non scientists.   "For every complex problem there is a solution which is simple, neat and wrong."  H. L. Mencken

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