12 THE ANALYSIS OF POTASSIC CHLORIDE. 



very much less, because the great mass of the nitric acid was eliminated 

 by the first crystallization. After the third recrystallization, the diphe- 

 nylamin reaction failed to reveal the presence of any retained nitrate. 



The precipitation was carried out in the following manner : The often 

 recrystallized, very pure potassic nitrate was dissolved in the least possible 

 quantity of cold water, contained in a platinum dish, packed in ice. 

 Slowly, in order to prevent warming, hydrochloric acid gas was run into 

 this solution. The gas was supplied by warming a pure concentrated 

 solution, and was passed into the nitrate solution through an inverted 

 platinum funnel. The potassic chloride, which appeared somewhat yellow 

 from its slight platinic impurity, was whirled in the platinum centrifuge, 

 and dissolved in purest water. Potassic chlorplatinate is practically insol- 

 uble in a concentrated solution of the chloride, as the law of concen- 

 tration effect and the theory of ionization predicts ; hence the impurity 

 was easily separated upon a small, pure filter. The clear, colorless solution 

 was again saturated with hydrochloric acid, and the same round of oper- 

 ations repeated. Upon a third repetition of this process, the nitric acid 

 was eliminated and the salt, as a rule, was wholly colorless in consequence. 

 On no occasion, even with large amounts of materials, did perceptible 

 color remain after five treatments. No specimen was subjected to less 

 than seven such recrystallizations, while some was passed yet five times 

 more through the precipitation and centrifugal drying. Assuming that 

 each time about three-quarters of the ordinarily adhering mother liquor 

 was removed by the centrifugal separation, these crystals must have been 

 as free from heteromorphous substances as if they had been recrystal- 

 lized many thousand times in the ordinary fashion. It will be shown that 

 all the samples gave the same results upon analysis, hence further puri- 

 fication according to this method was needless. The salt was found to 

 be wholly free from sodium by a sensitive spectroscopic test. It was in 

 every case freed from acid by a single recrystallization from the purest 

 water, and by fusion in the manner to be described later. 



Seven different samples were prepared after this fashion from varying 

 raw material. These are given in the list below. 



(a) The pure potassic material ("C. P." of German preparation) was 

 recrystallized as nitrate six times, and precipitated as chloride seven times. 

 This salt after the final recrystallization from pure water was dried in a 

 platinum dish at 120 in an electric oven. The salt was snow-white, and 

 was as clear as water when fused, as indeed, were all the other samples. 



(&) This sample was similar to a, but obtained by the evaporation of 

 the final aqueous mother liquor decanted from a. The mother liquor from 

 b was rejected. 



