1912.] PUBLIC DOCUMENT — No. 31. 33 



Prkcipitated Gypsum. 

 About 1870 the manufacture of double superphosphate was 

 uiidertakeu. The method consisted of extracting the raw phos- 

 phate with dilute sulfuric acid, and this solution was used again 

 for extracting another portion of the phosphoric acid. This 

 method left behind a large amount of gypsum which contained 

 about 1 per cent, of citrate soluble phosphoric acid. This resi- 

 due was sold to farmers at a low price, and was used to check 

 the escape of the ammonia from the manure. Experiments by 

 several iuA^estigators, particularly by Hansen, showed it to be 

 of no particular value for such a purpose. 



Gypsum-superphosphate and Supeephosphate. 



In Germany low-grade raw phosphates were treated with 

 sulfuric acid, and a product was secured containing 4-6-8 

 per cent, of soluble phosphoric acid, and this was called 

 gypsum-superphosphate. It was found that this material, if 

 used in sufficient amount, held fast the ammonium carbonate 

 present in the manure and checked the further action of the 

 bacteria. This was due to the action of the free phosphoric 

 acid. Sulfuric acid and ordinary superphosphate had a similar 

 effect. Because of the cost of such materials, however, their 

 use was not advised. 



SuLFUPvic Acid. 



After the use oi superphosphate had been discontinued 

 numerous experiments were made with quite dilute sulfuric 

 acid. A 2 per cent, solution of the sulfuric acid was sprinkled 

 over the manure before throv/ing it out, and also in the gutters 

 after its removal. The dilute acid was also mixed with peat 

 and sand before distributing it. Experiments by Maercker 

 and Pfeiffer showed that such treatment made the manure 

 sour, checked the loss of ammonia, and better results were se- 

 cured temporarily in the field due to the conserved nitrogen. 

 It was found, however, that one had to be very careful, other- 

 wise the feet and udder of the animal would be injured ; and, 

 furthermore, that the resulting manure had a bad effect upon 

 the physical character of heavy soils which required the addi- 



