APPENDIX I ' 351 



10 to 20 grms. 01 the soil are placed in a bottle of 500 to 1000 c.c. 

 capacity, together with 200 to 300 c.c. of approximately N/50 solu- 

 tion of calcium bicarbonate, and the air in the bottle is displaced 

 by a current of carbon dioxide in order to avoid possible precipita- 

 tion of calcium carbonate during the period of the determination. 

 The bottle is then placed in a shaking machine for three hours, after 

 which time the solution is filtered and an aliquot portion of the 

 filtrate is titrated against N/io acid, using methyl orange as indicator. 

 The difference in strength of this filtrate and that of the initial 

 solution represents the amount of calcium carbonate absorbed, each 

 cubic centimetre of N/io acid being equal to 5 mgs. calcium 

 carbonate. 



For a criticism of the method see E. A. Fisher (99) and for a 

 modification see F. J. Warth and M. P. Saw, Chemical Mem. Dept. 

 Ag. India, 191 9, 5, 157-172. For an account of the numerous other 

 methods see H. R. Christensen (67^). 



Hydrogen Ion Concentration, Ph value (see p. 115, and E. A. 

 Fisher (99)). 



Mineral Substances. — Complete analysis of a soil after the 

 silicates have been decomposed and the silica volatilised by treat- 

 ment with hydrofluoric acid is only rarely attempted. The British 

 method, adopted by the Agricultural Education Association, is thus 

 described by Hall : "20 grms. of the powdered soil are placed in a 

 flask of Jena glass, covered with about 70 c.c. of strong hydrochloric 

 acid, and boiled for a short time over a naked flame to bring it to 

 constant strength. The acid will now contain about 20*2 per cent, 

 of pure hydrogen chloride. The flask is loosely stoppered, placed 

 on the water bath, and the contents allowed to digest for about forty- 

 eight hours. The solution is then cooled, diluted, and filtered. 

 The washed residue is dried and weighed as the material insoluble 

 in acids. The solution is made up to 250 c.c, and aliquot portions 

 are taken for the various determinations. The analytical operations 

 are carried out in the usual manner, but special care must be taken 

 to free the solution from silica or organic matter" {The Soil). As a 

 rule only potash and phosphoric acid are determined, but where 

 necessary other bases are estimated in the usual way. 



Hissink ^ has discussed the value of strong HCl as a solvent in 

 soil analysis. American methods are described by F. E. Bear and 



^Internat. Mitt. Bodenkunde, 1915, 5, 1-24. For determination of iron see 

 Morison and Doyne, Journ. Agric. Set., 1914, 6, 97. 



