16 



Determination of Potash. Other 100 c.c. of the filtered extract 

 (equivalent to four grammes of fine earth) are boiled in a 300 c.c. Erlen- 

 ineyer flask, and 5 c.c. of a ten per cent, solution of barium chloride are 

 added, after which the determination is continued as in the first method. 



Phosphoric oxide is determined exactly as in Method I. 



METHOD IV. EXTRACTION BY HYDROCHLORIC ACID AT STEAM TEMPERATURE. 

 (HILGARD'S AND LOUGHRIDGE'S METHOD.) 



Fifty grammes of air-dried " fine earth " are placed in a porcelain, 

 beaker of sufficient size, 500 c.c. of hydrochloric acid of 1'115 specific 

 gravity are added, and 2 c.c. of nitric acid, and, after covering the beaker 

 with a clock glass, the mixture is digested on the steam bath for five days. 

 The solution is then filtered, the residual earth is thoroughly washed with 

 distilled water, the filtrate and washings are evaporated to dry ness, 

 as in Method I, with nitric acid in a shallow porcelain dish, and finally 

 made up to 250 c.c. 



Determination of Lime. 100 c.c. of the extract (equivalent to 20 

 grammes of fine earth) are placed in a 200 c.c. boiling flask, and pre- 

 cipitated by ammonia, as in Method I ; the flask is then filled up to the 

 mark with distilled water, and the contents filtered. 100 c.c. of the 

 filtrate (equivalent to 10 grammes of fine earth) are precipitated with 

 ammonium oxalate, as in Method I. 



Determination of Potash. 100 c.c. of the extract (equivalent 

 to 20 grammes of fine earth) are treated with barium chloride solution in 

 the same way as in Method I, and filtered into a 200 c.c. flask; after pass- 

 ing through the usual processes 100 c.c. of this (equivalent to 10 grammes 

 of fine earth) are taken, as in Method I, for the actual potash determina- 

 tion. 



METHOD V. EXTRACTION OF THE SOIL BY MEANS OF CITRIC ACID. 

 (DYER'S METHOD.) 



The solution here used is that recommended by Dr. Bernard Dyer, in 

 the " Journal of the Chemical Society," March, 1894, p. 141, which is an 

 adaptation of that previously used at the Halle Experiment Station, and 

 published by Maercker and Gerlach in 1892. In a rubber-stoppered three 

 litre flask are placed 200 grammes of dry-sifted " true soil " (i.e., as sifted 

 through a 3 mm. sieve), together with two litres of distilled water con- 

 taining in solution 20 grammes of pure citric acid. This solution is left 

 in contact with the soil, at the ordinary temperature, for seven days, 

 shaking the mixture thoroughly about fifty to sixty times each day. At 

 the end of the seven days the solution is filtered, by the aid of a filter 

 pump, through a porcelain funnel with a flat perforated base, or through 

 a Berkefeld candle filter; 500 c.c. of the filtrate would be required for 

 each of the determinations described below. 



Determination of Lime. 500 c.c. of the filtered soil extract (equivalent 

 to 50 grammes of soil) are placed in. a 1,000 c.c. flask, and a few drops of 

 rosolic acid are added, followed by ammonia, as in the previously described 

 lime determinations. The mixture is boiled, and, after filling to the mark, 

 it is filtered, and 500 c.c. of the filtrate, equivalent to 25 grammes of soil, 

 are warmed with a few drops of acetic acid in an Erlenmeyer flask, and 

 then treated with 50 c.c. of 4 per cent, ammonium oxalate solution, the 

 precipitate being collected, as before, after warming for six hours. 



Determination of Potash. 500 c.c. of the filtered extract (equivalent 

 to 50 grammes of soil) are evaporated to dryness in a platinum dish, and 

 cautiously ignited. The residue left in the dish is dissolved in hydroch- 

 loric acid, filtered into a 300 c.c. Erlenmeyer flask, and boiled. 5 c.c. of 

 10 per cent, barium chloride solution are added, and the determination 

 is proceeded with as in the method already described in connection with 

 the extraction by hydrochloric acid. 



