402Dr.Apjohn mi Bicyanide of Mercury and Iodide of Potassium. 



unnecessary to detail, it became obvious that the crystals were 

 composed of the two salts presented to each other. The next 

 object therefore, was to determine the relative proportions 

 in which these were united. To effect this, 40 grains of the 

 compound were dissolved in hot water, and a stream of sul- 

 phuretted hydrogen passed through the solution as long as 

 it threw down any precipitate. Ihis, (which by a previous 

 experiment was known to be bisulphuret of mercury,) when 

 perfectly dry, weighed 22*25 grains. Hence as 232 (atomic 

 weight of cinnabar) : 252 (atomic weight of bicyanide of mer- 

 cury) : : 22-25 : 24*16 = the bicyanide in the 40 grains. 



The solution from which the cinnabar was thrown down 

 was now evaporated to dryness, in order to expel the whole 

 oftheprussic acid formed; and to the residue, which by a 

 previous trial was found to be iodide of potassium, after being 

 dissolved in water, nitrate of silver was added as long as it 

 caused any precipitate. This (the iodide of silver) collected 

 upon a double filter, dried and weighed, amounted to 22*08 

 grains. Hence as 234 (atomic weight of iodide of silver) 

 : 164 (atomic weight of iodide of potassium) : : 22*08 : 15*47 

 = the iodide of potassium in the compound. The 40 grains 

 were therefore constituted as follows : 



Bicyanide of mercury 24*16 



Iodide of potassium 15*47 



39*63 



Now, as 24*16 : 15*47 are very nearly in the ratio of 252 : 164, 

 it is obvious that the compound consists of an atom of each 

 of its constituent salts. And as, by viewing these as destitute 

 of oxygen and hydrogen, we account for the entire 40 grains, 

 it is clear that they are present as bicyanide and iodide, not 

 as biperprussiate and hydriodate. This latter conclusion also 

 is confirmed by the salt yielding no water upon being heated 

 strongly in a glass tube. 



This compound, as far as my knowledge extends, is with- 

 out any perfect parallel in chemistry. It is a double salt, but 

 it is distinguished from all those with which we have been 

 long acquainted by the circumstance of the proximate con- 

 stituents of its component salts, both the electro-negative and 

 the electro-positive, being all different. Berzelius says (Traite 

 de Chimie, torn, troisieme p. 331): "On ne connait pas 

 d'exemple bien constate de sels qui renferment plus de trois 

 constituans." The hiatus here alluded to is obviously filled 

 up by the salt just described, and which, from its composition, 

 may be denominated the iodo-bicyanide of potassium and 

 mercury. 



It 



