46 CHEMICAL FERTILIZERS 



so that they show a theoretical percentage of more than 

 100 % of gypsum. 



The alkali soils of the United States and the usar soils 

 of India have been ameliorated by the addition of gypsum, 

 but the cost is somewhat great. Gypsum is rarely used 

 directly as a manure in Great Britain, because so much 

 calcium sulphate is applied in the form of superphosphate ; 

 in addition to which, in the vicinity of large towns, there is 

 a considerable quantity of sulphuric acid coming down 

 with the rain, so that sulphur compounds need not be used 

 as manure; there are, however, many instances of benefits 

 resulting from the agricultural use of gypsum. Gypsum is 

 used in the fertilizer industry to dry superphosphate ; 

 it is sometimes much appreciated by horticulturists, as it 

 helps to overcome the injury done to the soil by excessive 

 applications of sodium salts, introduced as nitrate of soda, 

 common salt and sodium carbonate. 



REFERENCES TO SECTION I. 



NITRATES. Hutchinson, " Saltpetre : its Origin and Extraction in India," 



Journ. Soc. Chem. Ind., 1917, p. 709. 

 Bryant, "A New Potash Supply," Journ. Soc. Chem. Ind., 1919, 



p. 360 T. 



PHOSPHATES. Robertson, " Notes on the Nature of the Phosphates con- 

 tained in Mineral Phosphates," Journal of Agricultural Science, 



vol. viii., Part I., p. 16. 

 Robertson, " Solubility of Mineral Phosphates in Citric Acid," Journal 



of the Society of Chemical Industry, 1914, p. 9, and 1916, p. 217. 

 " Egyptian Phosphate Resources." Journ. Soc. Chem. Ind., 1919, p. 187 R. 

 Soderbaum, " Experimental Results," Journ. Soc. Chem. Ind., 1914, 



p. 34- 

 "Phosphatic Deposits in Holland," Journ. Soc. Chem. Ind., 1919, 



p. 390 R. 

 POTASH. Kestner, " The Alsace Potash Deposits and their Economic 



Significance in Relation to Terms of Peace," Journ. Soc. Chem. Ind., 



vol. 37, No. 21, p. 291. 

 Cresswell, " Possible Sources of Potash," Journ. Soc. Chem. Ind., 1915, 



p. 388. 

 Smetham, " Manufacture of Potash from Felspar," Journ. Bd. Agric., 



1917, p. 1087. 

 Louis, " Mineral Production in Relation to the Peace Treaty," Nature, 



1919, p. 206. 

 Nishimura, " Potassium Chloride from Mother Liquor in Manufacture 



of Sea Salt," Journ. Soc. Chem. Ind., 1917, p. 1046. 

 Publications of the German " Kali-Syndicat." 

 Ross, " Extractions of Potash from Silicate Rocks," Journ. Ind. Eng. 



Chem., 9, p. 367- 

 Binder, " Les Mines en Alsace Lorraine," Journ. Soc. Chem. Ind., 1919, 



p. 218 R. 



