CHANGES IN INORGANIC CONSTITUENTS 423 



starvation. Thanks to the sulphur bacteria, the higher plants are 

 enabled to utilize again the sulphur once locked up in plant and ani- 

 mal tissues, and liberated thence by decay bacteria. The circulation 

 of sulphur is thus made possible and the cycle is completed when the 

 sulphates are again used by plants to build protein compounds. It 

 may also be noted in this connection that " Thiobacillus denitrificans " 

 described by Beyerinck, may also oxidize elementary sulphur. In 

 this case, however, the oxygen is derived from nitrates instead of the 

 atmosphere. Thus: 



6KN0 3 + 58 + 2 CaC0 3 = 3K 2 SO 4 + 2CaSO 4 + 2CO 2 + sN 2 



SULPHOFICATION. Lint has found that under optimum temperature 

 and moisture conditions, sulphur applied at the rate of 600 pounds 

 per acre was almost completely oxidized within ten weeks. Boullanger 

 and Dugardin in explaining the fertilizing action of sulphur on the 

 basis of its effect on the supply of available nitrogen found that am- 

 monification was increased by small amounts of sulphur, nitrogen- 

 fixation was not affected and nitrification was depressed. It has been 

 pointed out by Kossovitch, Brioux and Puerbet that the mechanism 

 of sulphur fertilization is very complex and that the oxidation of free 

 sulphur occurs entirely by bacterial and not by chemical means. 

 Brown and Kellogg have recently advanced evidence to prove that 

 soils have a definite sulphofying power which is determinable in the 

 laboratory by a newly devised method. They claim that the process 

 of sulphofication is mainly brought about by bacterial action, but 

 probably there is also a small production of sulphates in soils due to 

 chemical action. 



It has been observed that soils differentiated by various treatments, 

 vary widely in sulphofying power, the presence of organic matter being 

 responsible for an increase up to a certain point. Aeration and mois- 

 ture must be optimum for favorable sulphofication while the addition 

 of carbohydrates to soils depresses the process. 



SULPHATE REDUCTION. The fact that sulphates may be reduced to 

 sulphides in the presence of organic matter has been known for many 

 years. In compost heaps, and at the bottom of seas, lakes and rivers, 

 the reduction of calcium sulphate is of common occurrence. Similarly, 

 ferrous sulphate may be reduced in water-logged soils and in swamps 



