1894. J 75 



OLEATE OF COPPEE. 

 BT H. GTJAED K]S"AGGS, M.D., F.L.S. 



The error of considering the green cupric salt which forms on 

 the pins of greasy Lepidoptera to be verdigris (acetate of copper) 

 seems to be universal among entomologists. 



The salt is not verdigris, but a combination of oleic, stearic and 

 margaric acids with copper, which, for convenience sake, we may call 

 the oleate of copper, seeing that the last two acids are in compara- 

 tively small quantity. If any one would like to prove it experimentally 

 he has merely to scrape off some of the green salt and drop it into a 

 very hot silver or iron spoon, when his nostrils will be assailed with 

 a greasy vapour of an excessively offensive odour. The oleate of 

 copper of the Materia Medica, which does not contain the margaric 

 and stearic acids (these having been eliminated by freezing), will 

 yield precisely the same result. But verdigris, if similarly treated, 

 will emit not unpleasant fumes of vinegar, and the operator will 

 probably exclaim "pickles." 



Another experiment may be tried by dissolving verdigris in water, 

 first cold then boiling, in a test tube, and adding a solution of carbonate 

 of soda, when a dense precipitate of carbonate of copper will be 

 thrown down. But if we apply this same treatment to the green salt, 

 we shall fail to make the salt mix with, or even tinge, the water ; the 

 only result of furious boiling will be to melt the salt, cause it to float 

 as an oil on the surface, and splutter up against, and adhere to, the 

 sides of the tube above high water mark ; and carbonate of soda will 

 have no effect upon it whatever. Ordinary oleate of copper behaves 

 in the same manner. 



The formation of the green salt probably takes place as follows : 

 the oleic acid is in feeble combination with glycerine, but this it 

 forsakes for metal for which it has a greater afiinity. The metal is 

 first oxidized, either by the acid fluids of the insect, by the atmo- 

 sphere, or by the oleic acid itself, the process being possibly aided 

 by galvanic action set up by contact of acid matter with the copper 

 and zinc of the alloy ; and subsequently this salt is formed, the libe- 

 rated glycerine keeping it company, although released from its chemical 

 combination. 



London : February 2Hd, 1894. 



