EFFECT OF CONCENTRATION 571 



may be substituted for the potassium in the washed product. 

 In the official method, moreover, there is danger of securing a 

 final precipitate which may contain traces of calcium and mag- 

 nesium sulfates when these bodies are abundantly present in the 

 sample used for analysis. The careful analyst must guard 

 against these sources of error, but it is probably true that he 

 will never secure a practically chemically pure precipitate of 

 potassium platinochlorid when working on the mixed fertilizers 

 found in commerce. 



482. Effect of Concentration on the Accuracy of Potash Analy- 

 sis. Winton has also studied the sources of error in the deter- 

 mination of potash as platinochlorid, especially with reference 

 to the effect of the concentration of the solution at the time of 

 precipitation. 51 



He finds that the method of precipitating in concentrated 

 solutions and drying the potassium platinochlorid at 130, depends 

 for its accuracy upon the mutual compensation of three errors; 

 viz., ( i ) due to the solubility of the potassium salt in 80 per cent, 

 alcohol, (2) due to the presence of water in the crystals which is 

 not driven off at 130, and (3) due to the use of a factor based 

 on the wrong atomic weight of platinum. 



He finds, further, that the error due to the presence of water 

 occluded in the crystals can be reduced to a minimum, and the 

 process of drying greatly simplified, by adding the solution of 

 platinum chlorid to the potash solution in a dilute condition, not 

 exceeding one per cent, in strength. The potassium platinochlo- 

 rid thus produced can be very effectively dried at 100. The 

 error due to the solubility of the salt in 80 per cent, alcohol can 

 also be greatly reduced by using 95 per cent, alcohol. The error 

 due to the wrong factor; viz., 0.3056 based on the old atomic 

 weight of platinum, can be corrected by using the factor based 

 on the recently determined atomic weight of platinum; viz., 195, 

 which is 0.30688. 



Since Winton's paper was published the atomic weight of plati- 

 51 Journal of the American Chemical Society, 1895, 17 : 453. 



