572 AGRICULTURAL ANALYSIS 



num has been reduced to 194.8, so that the factor on this basis 

 is 0.3071. 



483. Differences in Crystalline Form. Winton has also ob- 

 served a distinct difference in the crystals of potassium platino- 

 chlorid when obtained from concentrated and dilute solutions. 52 

 When platinic chlorid is added to a concentrated solution of 

 potassium chlorid, a large part of the salt which is formed is 

 precipitated in a pulverulent state, the remainder being depos- 

 ited on evaporation. After treating with alcohol, filtering, and 

 drying, the double salt is found in the state of a fine powder 

 which, when examined under the microscope, is found to consist 

 largely of radiating crystals. The characteristic form is one 

 having six arms formed by the intersection, at right angles, of 

 three bars. Numerous globular cavities in the crystals are ob- 

 served in which mother liquid is enclosed. For this reason the 

 salt is not easily dried at 100, but when so dried loses additional 

 moisture at 130, and still more at 160. The total additional 

 loss, after drying at 100, from this cause may amount to as 

 much as six-tenths per cent, of potassium chlorid. 



When, however, the solution of the potassium salt is so dilute 

 that no precipitate at all is formed on the addition of platinic 

 chlorid, the double salt is all deposited, as well as formed slowly, 

 during the evaporation and occurs exclusively as octahedra. These 

 octahedra are comparatively free of cavities, and give up practical- 

 ly all their moisture when dried at 100. A method of proced- 

 ure, therefore, for potash determination, based on the above prin- 

 ciple of the addition of the reagent to dilute solutions, and dry- 

 ing the double salt produced upon evaporation, after washing 

 with 95 per cent, alcohol at 100, and using the factor 0.3071 

 for potassium chlorid and 0.1941 for potassium oxid, gives good 

 results and is regarded as better than any of the methods which 

 prescribe the addition of platinic chlorid to highly concentrated 

 potash solutions. 



484. Factors for Potash Estimation. The factor now in use 

 by the official chemists to convert potassium platinochlorid into 

 potash (K 2 O) is 0.1941, and for potassium chlorid 0.3071. 



M Journal of the American Chemical Society, 1895, 17 : 453- 



