Dec. IS.I9I9 Oxidation of Sulphur in Soils 343 



however, when tried in compost experiments equaled the soil used in the 

 large experiments in its capacity to render phosphate soluble. 



That the solubility of the phosphate has been caused by the oxidation 

 of the sulphur is demonstrated by the parallel rise in acidity and sul- 

 phates found. 



Computing from November, 191 7, when the starter was added in the 

 earlier work and when for the first time active sulphofication was shown, 

 the duration of the earlier experiments as well as of the latter was 17 

 months. On the basis of 100 pounds water-free composts, it will be 

 seen that about 2^ pounds of phosphorus were made citrate-soluble in 

 No. 4 and 2X pounds in No. 6 and 10. The advantage in favor of No. 4 

 may be due to either the manure or the larger mass of soil and probably to 

 both. Taking into account the cost of materials, it appears that No. 4 

 is the more desirable compost. 



It is the writer's opinion that the presence of some manure and more 

 soil would have been advantageous in the later work because it prob- 

 ably would have provided a means of increased bacterial action as well as 

 assisted in maintaining the moisture content. 



It would appear from the work described here that while this procedure 

 would furnish a means for the manufacture of acid phosphate in an 

 emergency such as confronted us at the time, under ordinary conditions 

 the average consumer would object to the time and labor involved. Aside 

 from this, however, it is of scientific interest; and as better methods of 

 inoculation are developed the process may be so simplified that it may 

 become of immediate practical benefit. 



SUMMARY 



(i) Compost experiments of rock phosphate, sulphur, soil, and manure 

 show, after 24 months' time, that about 17 and 84 per cent of the total 

 phosphorus had been converted into a water-soluble and ammonium- 

 citrate-soluble form, respectively. Whether the amounts were really 

 larger than the above could not be determined because of the limitations 

 of the method. 



(2) Sulphofication did not proceed as rapidly as when an inoculation 

 was made with the sulphofying organism, and when this was done the 

 time of the sulphofication may be considered to be reduced nearly one- 

 third. 



(3) Composting under the same conditions but omitting the sulphur 

 also showed favorable results in rendering the soil phosphate or that added 

 in rock sulphate soluble, but not to the same extent as when sulphur was 

 present. 



(4) Nitrification was found to proceed to a certain extent regardless of 

 the acid formed by the sulphur oxidation. The amounts of nitrogen 



