The Erroneous Melting Point of Anhydrous Cupric Sulfate HERMAN A. LIEBHAFSKY Geneml Eleetrie Company, Seheneetody, New York
WAS surprising to learn that anhydrous cupric ITsulfate supposedly melts a t 200°C. ( I ) , reassuring to see in a 10-minute experiment that it does not, disconcerting to discover how many authorities say it does (1,2, 3, 4, 5), and comforting to find that at least two have the matter straight (6, 7). Under atmospheric pressure, anhydrous cupric sulfate does not melt, but it begins to decompose appreciably-presumably by loss of sulfur trioxide-at temperatures above GOO°C. The error must have sprung from a highly questionable rendering of a paragraph by Hodgkinson and Trench ( 8 ) , which is worth quoting, not only in the present connection, but also because it may point the way to interesting research in the chemistry of nitrogen. The paragraph reads: . Undoubtedly the most interesting salt examined is cupric sulphate. Either dry or with crystal water, the salt absorbed much NH., and then melted below 200". turned black, and as the temperature rose appeared t o boil, and finally a t somewhere about 400' began to decompose with incandescence, leaving almost pure metallic copper.
A hypercritical grammarian unfamiliar with chemistty might be excused for concluding from this quotation that anhydrous cupric sulfate melts below 200"; but no one is justified in naming this temperature as the melting point. No inorganic chemist should fail to realize that cupric sulfate, once it has absorbed ammonia, is cupric sulfate no longer. How could any chemist ever believe that anhydrous cupric sulfate, a
well-behaved, stable substance, "melts below 200'" grows black, then appears to boil, and decomposes near 400°, glowing (in the process) and leaving a residue of almost pure copper"? (5) It is true that Hodgkinson and Trench did not reach the ultimate in clear writingthat is, to write what cannot possibly be misunderstood-but how many of us ever do? Finally, i t is well to point out that the reference to the work of Hodgkinson and Trench is garbled in the Zentralblatt (9) in an abstract otherwise substantially correct. LITERATURE CITED
(1) HODGMAN, "Handbook of Chemistry and Physics," 27th ed.. Chemical Rubber Publishing Company. Cleveland, Ohio. 10d7 - - - - , yn. 291
(2) "International Critical Tables," McGraw-Hill Book Company, Inc., New York, 1926, vol. I , p. 122. (3) LANCE,"Handbook of Chemistry," 5th ed., Handbook Publishers, Inc., Sandusky, Ohio, 1944, p. 186. (4) OLSEN,"Van Nostrand's Chemical Annual," 7th issue. D. Van Nostrand Comnanv. Inc.. New York. 1934. o.230. (5) FRIEDHEIMAND ~ ~ ~ & R ~ : ' " ~ m e l i n - ~ r~aauntd' ;b u c hder anorganischen Chemie," Carl Winter's Universit%tshuchhandlung, Heidelberg, 1909, vol. V, part 1, p. 841. fRI LATIMER A N D HILDEBRAND. "Reference Book of Inoreanic Chemistrv." rev. ed.. The Macmillan Comoanv. . .. k e w York, 1940, p. 526. (7) MELLOR, "A Comprehensive Treatise on Inorganic and Theoretical Chemistry," Longmans, Green and Company, London, 1923, vol. 111, p. 241. AND TRENCH,Brit. ASSOC.Advmcemexl Sci. (8) HODCKINSON Rep.. 62nd meeting, 675+, (1892). (9) Ckem. Zentr., 11, 961-2, (1892). ~~~
