70 Messrs. Glassford and Napier on the metallic Cyanides. 



ride of silver. It is mentioned in Prof. Graham's * Elements 

 of Chemistry,* upon the authority of Prof. Liebig, that the 

 chloride of silver is soluble in cyanide of potassium, and that 

 the solution yields a double salt by evaporation. We have 

 repeatedly tried to obtain this double salt, but cannot say we 

 have been successful ; it requires two equivalents of cyanide 

 of potassium to obtain the chloride apparently in solution, 

 which then contains chloride of potassium and cyanide of 

 potassium and silver: by repeated crystallization and taking 

 the first crop, we get the latter salt free from the former, 

 which was determined by dissolving some of the crystals thus 

 purified ill water and saturating the solution with nitrate of 

 silver. The precipitate being afterwards boiled in sulphuric 

 acid, as noticed in a former part of the present paper, the 

 whole precipitate was dissolved, which would not have occur- 

 red had any chloride been present. 



It is upon this superior power of silver to combine with 

 cyanide of potassium to form the double salt just described, 

 that we have adopted the method of determining the per-cent- 

 age of cyanide of potassium in any sample. Nitrate of silver 

 is dissolved in distilled water to such a strength, that two gra- 

 duations of a common alkalimeter will contain exactly 1 grain 

 of nitrate of silver ; 25 grains of the sample to be tried are 

 dissolved, and this solution of nitrate of silver is added cau- 

 tiously until the precipitate formed ceases to be redissolved ; 

 the number of graduations of the silver solution taken are noted, 

 and calculated according to the following equation : — as 170 is 

 to Q5'5 so is the number of graduations taken, to the answer, 

 which must be multiplied by 4 to obtain the per-centage. Ni- 

 trate of silver of any strength may be used without a graduated 

 measure, but the solution must in that case be evaporated to 

 dryness, treated with hydrochloric acid, again evaporated to 

 dryness, and fused to know the quantity of silver taken ; the 

 amount of cyanide of potassium may be known by the following 

 calculation : — As lOS'O is to 131*08 (2 equivalents of cyanide 

 of potassium), so is the weight of silver obtained multiplied 

 by 4 to the per-centage of cyanide of potassium in the sample. 



The substitution of cyanide of potassium for any other 

 substance which may be in union with silver is beautifully 

 shown by adding cyanide of potassium to ferrocyanide of sil- 

 ver: it requires 4 equivalents of the former to 1 of the latter 

 to produce 2 equivalents of cyanide of potassium and silver, 

 and 1 of ferrocyanide of potassium ; the solution being eva- 

 porated the two salts crystallize distinct, and may be easily 

 separated both by their shape and colour. In some expe- 

 riments of this kind we have been able to recover within one 



