30 



For this work and the soil investigation to be described later 

 two solvents were selected, namely, i per cent citric acid solu- 

 tion, and hydrochloric acid. The first has already been re- 

 200 



ferred to , but for soil work the conditions attending its use were 

 modified somewhat. 



Hydrochloric acid - - was recently proposed by Moore 1 for 



the determination of available mineral plant food in soils. In the 

 work referred to pot experiments were made with a large variety 

 of soils, and the amounts of phosphoric acid extracted by the 

 solvent in question agreed closely in nearly all cases with the 

 actual amount removed by the crops. 



The solubility determinations with the reagents selected 

 were carried out in the following manner. The ratio of solvent to 

 substance was 500 c.c. to 100 grams. These were placed in a 

 litre glass stoppered bottle, and kept at a temperature of 40 de- 

 grees C in a water bath for exactly five hours. The bottles were 

 shaken every fifteen minutes. After the digestion the whole was 

 shaken and emptied on to a folded filter sufficiently large to hold 

 the entire contents of the bottle. After draining, 400 c.c. of the 

 filtrate representing 80 grams of the soil, were evaporated to 

 dryness. In the case of the citric acid the residue was treated 

 with magnesium nitrate solution, evaporated to dryness, and 

 ignited until all organic matter was destroyed. These residues 

 were taken up with water and nitric acid and the phosphoric 

 acid determined. 



In all the experiments a preliminary digestion was made 

 with 20 grams of soil and 100 c.c. of the solvent, in order to 

 determine the basicity of the soil. A correction was then made 

 in the strength of the acids so as to reduce the solvent action to 

 a uniform basis. 



Portions of the artificial soil described were air-dried and the 

 solubility of the phosphoric acid determined. Lime (one and 

 two grams) was mixed with other portions and the action allowed 

 to go on for seven days, the mixture being kept moist during the 

 meantime. These mixtures were then air-dried and solubility 

 determinations made. The following results were obtained. 



i Jour. Am. Chem. Soc., 1902, 79. 



