POTASH METHODS 545 



what quantity of chlorid of platinum should be added in order that 

 it will be in slight excess. The quantity of the platinum reagent 

 used is calculated in such a way that it is sufficient to saturate 

 the whole quantity of the salts present, which are for this purpose 

 calculated as if they were the chlorid of sodium. The chlorid of 

 platinum employed should contain in 100 cubic centimeters 17 

 grams of platinum. Each cubic centimeter of the solution is suffi- 

 cient for each decigram of the weight of the saline residue obtain- 

 ed as above. After adding the platinum salts the mixture is placed 

 in a capsule and evaporated with precautions to prevent the plati- 

 num salt from being heated beyond a temperature of 100. Above 

 this temperature the salts may form a little of the subchlorid of 

 platinum which is insoluble in alcohol. After cooling, the mass 

 is digested for several hours with 15 cubic centimeters of 95 per 

 cent, alcohol, the capsule being placed under a small cover. Dur- 

 ing this time it is stirred from time to time with a glass rod and 

 the supernatant liquid is poured into a small filter and the salt 

 washed with alcohol until the filtrate becomes colorless. There is 

 thus obtained as an insoluble residue a mixture of chloro-platinate 

 of potassium with various quantities of soda, silicates and oxids 

 of iron which may have been present in the original sample. 

 By means of boiling water the mass remaining in the capsules 

 is dissolved and poured upon the filter and the washing of the 

 capsule is continued with boiling water until all of the chloro- 

 platinate is dissolved, which is easily determined by the alcohol 

 wash becoming colorless. The solution of chloro-platinate is re- 

 ceived in a well glazed dish, containing no cracks, and is heated 

 upon a sand bath to boiling and there is added to it in very small 

 proportions some formate of soda dissolved in water. The cap- 

 sules having been taken from the bath to avoid mechanical loss, 

 formate of soda is added until the mixture is completely decolor- 

 ized. Instead of doing this in an ordinary' dish, an open flask or 

 beaker may be employed. By this process the platinum present 

 in the mixture is precipitated as a black powder, and in order to 

 aggregate it, the mixture is evaporated to about one-half its vol- 

 ume and brought upon a small filter, bringing the platinum in by 

 means of cold water slightly acidulated. When all the platinum 

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