54O AGRICULTURAL ANALYSIS 



for practical purposes will be quite sufficient, may be secured by 

 clipping a platinum wire loop into a strong acid solution of the 

 supposed potash compound, and viewing through a piece of cobalt 

 glass, the coloration produced thereby when held in the flame of 

 a bunsen. The red-purple tint thereby produced is compared 

 with that coming from a pure potash salt similarly treated. If 

 a fertilizer sample give no indication of potash when treated as 

 above it may be safely concluded that it does not contain any 

 weighable quantity. 



For the estimation of the percentage of potash present in a 

 given sample it may be safely assumed that all of value in agri- 

 culture will be given up to an aqueous or slightly acid solution 

 if organic matter have been destroyed, as indicated in a pre- 

 vious paragraph. In the case of minerals insoluble in a dilute 

 acid, the potash may be determined by some one of the processes 

 given in the first volume. 



The potash having been obtained in an aqueous or slightly 

 acid (hydrochloric) solution, it may be determined either by 

 precipitation as potassium platino-chlorid or as potassium per- 

 chlorate. The former method is the one which has been almost 

 exclusively used by analysts in the past, but the latter one is 

 coming into prominence, and by reason of the greater economy 

 attending its practice and the excellent results obtained by some 

 analysts, demands a generous consideration. 



462. The Platinic Chlorid Method. The principle of this 

 method rests on the great insolubility of the potassium platino- 

 chlorid in strong alcohol and the easy solubility of some of its 

 commonly attending salts ; viz., sodium, etc., in the same re- 

 agent. Before the precipitation of the potash it is customary to 

 remove the bases of the earths, sulfates, etc. Barium chlorid 

 and hydroxid, ammonium oxalate or carbonate, sulfuric acid, etc., 

 are used in conjunction or successively to effect these purposes 

 in the manner hereinafter described. The filtrate and washings 

 containing the potash are evaporated to dryness and gently ignited 

 to expel ammonium salts and in the residue taken up with water 

 and acidulated with hydrochloric acid, the potash is precipitated 



