No introductory organic chemistry laboratory curriculum would be complete with out a synthesis known as the Grignard, which involves halo-benzene and magnesium shavings. A Grignard is hard to initiate; one must slightly pulverize the magnesium to expose unoxidized metal, thus enabling the reaction to proceed.

A Grignard must be nursed along at first with the heat from one's palm, but once it gets going, a Grignard can be hard to stop. Unattended reaction vessels may explode or shoot contents all over the ceiling. An ice bath is the best way to control the rate of reaction, but too much cooling can stop the process altogether.

The potential for exponential rate increase for a phenomenon is observed in many biological and physical science contexts. Seldom are such scenarios as simple as the "snowball effect", but are more often subject all sorts of perturbations.

Where exponential rate increase is unimportant, accumulations of critical amounts of material may be extremely important (examples would include gas/air mixtures reaching explosive ratios, or the accumulation of poisons by plants and animals). A toxicologist once told me that aspirin overdoses are particularly tricky. More than once, patients admitted to ER have been treated and sent home feeling fine, only to be found dead the next day. But I won't belabor the analogy...

-- james hyde (hydesci@gte.net), January 03, 2000

Answers

Excellent. Thank you.

-- M.C. (mountaineer60@juno.com), January 03, 2000.

The true mystery of the Grignard reaction is that when you cannot initiate it in your carefully dried vessel, you simply mix together open test tube -- the "Minnie Grinnie" -- will start it every time.

Maybe we will crash and burn -- the classic Grignard rxn -- while Italy will be just fine -- the Minnie Grinnie.

How's that for stretching your metaphor.

-- Dave (aaa@aaa.com), January 03, 2000.