60 Messrs. Glassford and Napier on the 



be nearly 1 eq. of anhydrous carbonate of potash to 1 eq. of 

 the anhydrous ferro-cyanuret of potassium. The process is 

 very productive, for the weight of the cyanuret of potassium 

 obtained by this process is much greater than the weight of 

 the cyanuret obtained by heating ferro-cyanuret of potassium 

 alone, owing to the cyanogen of the cyanuret of iron uniting 

 with the potassium contained in the carbonate of potash ; and, 

 moreover, the process occupies less time. Some carburet of 

 iron always remains in the crucible." 



6. Cyanide of potassium may be obtained pure for experi- 

 mental investigation in the laboratory by the use of absolute 

 alcohol ; but where hundred weights are prepared and used 

 at a time this is not admissible. As employed in the arts it 

 contains many impurities: these are chiefly cyanate, carbonate, 

 muriate and sulphate of potash, silica, and yellow prussiate of 

 potash. The average amount of these impurities is 35 per 

 cent., often as high as 50 per cent. It contains much silica 

 when prepared, as is usually directed, in earthenware cruci- 

 bles ; and when the exact proportions of the yellow prussiate 

 of potash or carbonate of potash are not employed; when 

 these are not perfecdy anhydrous, salts of ammonia are gene- 

 rated ; and when commercial carbonate of potash is used, mu- 

 riate and sulphate of potash. Even when the materials are 

 employed chemically pure and perfectly anhydrous, it contains 

 20 per cent, of cyanate of potash ; this, according to Professor 

 Liebig, is of little consequence in the ordinary operations of 

 testing, but in respect to analytical inquiry, and to electro- 

 metallurgical operations, we find it of the greatest importance. 

 As however we shall have opportunities of pointing these out 

 in detail, we only allude to them here in a general way. 



7. When nitrate of silver is added to solution of cyanide of 

 potassium, just so long as the precipitate which is at first 

 formed is redissolved, we obtain the whole of the cyanide of 

 potassium in union with the silver, none of the other salts 

 present, although amounting to a large per-centage, taking 

 any part in the action. Upon this law we have founded a 

 method of estimating the exact quantity of pure cyanide of 

 potassium in any sample ; as, however, the principle upon 

 which this depends can be better explained when the nature 

 and constitution of the cyanide salt of silver is described, we 

 shall return to it when treating of that metal. 



8. As when one eq. of chloride of gold combines with one 

 eq. of chloride of potassium, a double salt, called chloride of 

 gold and potassium, is formed, so shall we call the union of 

 one eq. of cyanide of gold with one eq. of cyanide of potassium 

 the "cyanide of gold and potassium," and apply similar names 

 to the other metallic salts having a like constitution. The 



