Diazonium Salt Safety
To the Editor: I n a recent Letter to the Editor [J. CHEM.EDUC. 48, 640 (1971)], Mr. E. R. Trumbull described the uncontrollable decomposition of an aqueous diazonium salt solution after the addition of iodide ions. Since we have had similar annoying experiences when treating a lot of different diazonium salt solutions according to the published general procedures, I think it is time to correct a typical textbook error involved here. The normal procedure to synthesize iodo compounds from aromatic diazonium salts involves the addition of a sodium or potassium iodide solution to the ice cold solution of the diazonium salt. But, since in this case the incipient exothermic decomposition takes place in the presence of a vast excess of the very energy rich substrate there is always a high (Continued on page 146)
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chance tabat,:un unc~mtrollablcchnin reaction c:~nbc initiated. If, ou tlic other hand, the dinzonium snit, solution is added to t,he iodide solutiou in more or less small portions it is always assured that only smnll amount,s of t,hc poteudially dangerous material are dccomposcd at, onc t,ime. Incideut,ally, this procedure is prescribed in the 1iterat)ure several times; even additions of the cooled diazonium salt solution to hot solut,ions of dkali metal iodide solutions are reported. I call see therefore no reason why one should not abaudou totally the pot,ent,iallydangerous addition of iodide to diazonium salt in favor of the safe reverse addit,ion of diazonium salt solutions to solutions of iodides. DIETERHELLWINKEL INSTITUT DKR UNIVIRSTAT
O ~ O A N ~ S CCHI;MISCIII.:S H
69 HIIIDI:LBIIIIG. W. GIIHMANY
The chemistry of a Cooling Drink
To the Editov: I do not tbiuk that Dr. N. A. Daugherty has satisfactorily explaiued \~-hyice cubes fuse together (J. CHEM.E ~ u c .48,173, , March, 1971). I n an alcoholic There are, as I see it, t , ~ reasons. o drink, like whiskey on the rocks, t,he alcohol lowers the freezing point of t,he solution, and actually cools the ice cubes to about -10°C. The pure melt water between t,he ice cubes freezes t,he cubes t,ogether as the below freezing temperature permeat,es the ice. But alcohol is not. necessary. A bucket of ice cubes will also fuse together, merely from t,he pressure of the cubes on one another. The sheer weight, of the cubes lolvers the freezing point of vater (by Le Chatelier's Principle) and a film of ~vaterwill appear between the cubes where they are in contact. As the pressure is reduced, by the melting of the ice, the freezing point slowly rises, and the melt water between the cubes freezes. GUSTAV ALBRECHT CALIFORNIA INSTITUTE: OF TI~CHNOLOGY CALIFORNIA 91109 PASADDNA,
Protecting Dewar Flasks
To the Editor: A cheaper alternative to Michael Dymicky's suggestion [J. CHEM.EDUC.,48, 397 (1971)l for protecting Dewar Flasks is to use ordinary wide-necked "thermos" bottles, which are even better protected, have handles and covers, and are easily available at about one-third the cost of the "laboratory" variety.
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