562 AGRICULTURAL ANALYSIS 



to be as carefully avoided as possible since these crystals inter- 

 fere with the subsequent operation. The crystalline residue is 

 rubbed to a powder with a broad glass rod and then treated with 

 20 cubic centimeters of alcohol and vigorously stirred and rubbed 

 and the solution filtered through a warm filter previously dried 

 to a constant weight at from 120 to 130 and moistened 

 with alcohol. Care is to be taken that the liquid does not touch 

 the edge of the filter. This operation is repeated two or three 

 times upon the residue remaining in the dish until all the soluble 

 platinum double salts are dissolved. Favorable results will be 

 secured the sooner if at the time of the second treatment with 

 arcohol the dish is heated until the alcohol is almost boiling. A 

 less content of platinum chlorid is not secured in this way because 

 by means of the first decantation by far the greater part of those 

 bodies are removed which are apt to reduce a solution of potas- 

 sium chlorid in alcohol. The well-washed precipitate is collected 

 upon the filter and, after as complete as possible a removal of 

 the alcohol by suction and by pressing between filter paper, dried 

 at 120 to 130, to constant weight. Usually 20 minutes are suf- 

 ficient for that purpose and the mass is weighed while still warm. 

 Before drying, the filter is carefully folded so as to avoid any 

 loss of material in weighing. Each milligram of potassium cor- 

 responds to one-tenth per cent, of potassium chlorid or potassium 

 sulfate. 



474. The Barium Oxalate Method. The principle of this pro- 

 cess, worked out by Schweitzer and Lungwitz 42 is based on the 

 fact that in an ammoniacal solution, by means of barium ox- 

 alate, all the alkaline earths can be precipitated as oxalates, 

 and sulfuric acid in similar circumstances can be thrown down 

 as a barium salt and the iron and alumina as hydroxids. The 

 reagents used to secure this precipitation are ammonia and barium 

 oxalate. 



For the determination of potash in a superphosphate the analyt- 

 ical process is conducted as follows. Ten grams of the super- 

 phosphate are mixed with half a liter of water and 15 grams 

 of barium oxalate dissolved in hydrochloric acid. 

 41 Chemiker-Zeitung, 1894, 18 : 1320. 



