43 



The weight of the potassium chloride multiplied by 0.63190 will give 

 that of the potash. K 2 O, in the 2 grains of air-dried soil. 



The weight of the sodium chloride present multiplied by 0.53043 will 

 give that of the soda, Xa 2 O, present in 2 grams of air-dried soil. 



The weights of the potassium platinum chlorides found in the dupli- 

 cate analysis should agree to a tenth of a milligram. 



Care must be taken that the barium hydrate used does not contain 

 either of the two alkalies, potassium or sodium. 



DETERMINATION OF THE SODA. 



The soda may be determined directly, instead of by difference, as 

 follows : Evaporate the filtrate and washings from the precipitate of 

 potassium platinum chloride to dry ness on the water-bath, and when dry 

 burn at a low red heat. The solution contains the sodium platinum 

 chloride, with the excess of the platinum tetrachloride used. A mixt- 

 ure of platinum and of sodium chloride is thus obtained ; on dissolving 

 in warm water and filtering, the sodium chloride present is washed out. 

 The filtrate is evaporated to dryness on the water-bath in a weighed 

 platinum dish, dried at 100 C. in an air-bath, cooled in a desiccator, and 

 weighed. The increase in weight is due to the sodium chloride present 

 in the 2 grams of air-dried soil. This is calculated to soda, as above. 



DE1ERMINATION OF THE SULPHURIC ACID. 



In the remaining 100 c. c. of solution B, equal to 2 grams of the air- 

 dried soil, the sulphuric acid is determined as follows: Heat the solu- 

 tion to boiling, and add 10 c. c. of barium chloride, prepared by dis- 

 solving 1 part by weight of barium chloride in 10 parts of distilled 

 water, and continue boiling three or four minutes. Allow the precipi- 

 tate to settle, decant the clear fluid on a weighed Gooch crucible, pour 

 50 c. c. of boiling water on the precipitate, allow to settle, and decant 

 as before. Finally transfer the precipitate of barium sulphate to the 

 crucible, and wash well with hot water. Dry, ignite strongly, cool, and 

 weigh. The increase in weight is due to the barium sulphate. This 

 weight multiplied by 0.34331 will give the weight of the sulphuric acid, 

 SO 3 , present in the 2 grams of air-dried soil. (Fres., 132, 1.) 



TREATMENT OF THE SOIL WITH NITRIC ACID (Sp. gr. 1.20). 



Treat 10 grams of the air-dried soil, previously burnt to destroy or- 

 ganic matter, with 200 c. c. of nitric acid, sp. gr. 1.2, in a porcelain 

 dish, heated to 100 C. on the steam bath for five days, and proceed in 

 the same manner as already given in the treatment with hydrochloric 

 acid, p. 35, to separate the* insoluble residue, and then the soluble 

 silica, taking care to wash the residue well with hot water. 



Make the filtrate from the soluble silica up to 500 c. c. 



