Mr Johnston on the Cyanide of Mercury. 11 9 



Art. XIX. — On the atomic constitution of the Cyanide of 

 Mercury. By J. F. W. Johnston, M. A. Communicated 

 by the Author. 



The admirable researches of Gay-Lussac have long ago shown 

 the true constituents of the cyanide of mercury, — that it con- 

 sists of the metal combined with cyanogen, and that when re- 

 solved into its ultimate elements by direct analysis, the gaseous 

 products, with the exception of a little hydrogen derived from 

 moisture or prussic acid retained between the plates of the salt, 

 are carbonic acid and azote in the proportion of two volumes of 

 the former to one of the latter. But though its constituents be 

 thus correctly made out, I am not aware that any chemist has 

 determined by experiment the atomic constitution of this salt. 

 It is usually called the Cyanide of mercury ; but I find it no- 

 where stated whether the constituents exist in it atom to atom, 

 or in what other ratio they are combined. The following ex- 

 periments clear up this point, and show the salt to be a Bi-cy- 

 anide : — 



1. Five. grains of the dry salt in fine powder mixed with 

 peroxide of copper and heated to redness in a glass tube by 

 the flame of a spirit lamp till gas ceased to come over, gave in 

 four experiments the following results : — 



Carbonic acid. Azote. Cyanogen. Atomic proportion. 



No. 1, 3.99 inches. 1.8 1.995 7.0 



2, 3.73 1.77 1.865 6 A 



3, 3.7 1.7 1.85 6.37 



4, 3.73 1.74 1.865 6.4 



Mean atomic proportion, 6.54 grs. 



The third column containing the volume of cyanogen whose 

 elements are given off, is simply half the volume of carbonic 

 acid obtained. For the volume of azote being always less 

 than half that of the carbonic, probably from the formation of 

 some nitrous compounds, this mode of estimating the cyanogen 

 has the less chance of error. 



