28 AGRICULTURAL EXPERIMENT STATION. 



Nitrate of soda, a compound of nitric acid (aqua fortis) and 

 soda, and sulphate of ammonia, a compound of sulptiutic acid (oil 

 of vitriol) and ammonia, are two of the most valuable nitrogenous 

 materials which are used to supply nitrogen to the farmer. Their 

 nitrogen is immediately available for use by the plant, the nitric 

 acid of the one and the ammonia of the other being the compounds 

 of nitrogen which largel}' serve as plant-food. 



The following materials furnish organic nitrogen to fertilizers : 



Dried blood, dried and ground fish, azotin and ammonite (pre- 

 pared animal matter), fish scrap, meat scrap, cotton-seed meal, 

 castor pomace, horn, hair, wool, leather waste, etc. These 

 substances must decompose and the nitrogen become changed into 

 compounds of nitric acid and ammonia before it is largely available 

 to plants. There is, therefore, a great difference in the value of 

 organic nitrogen as found in the above-named materials. Dried 

 blood, for instance, decomposes in the soil rapidly, while horn, 

 hair, wool and leather scrap in their natural condition decay very 

 slowly, and the nitrogen which they contain becomes useful only 

 after a long period of time. These latter substances are not only 

 less useful to the farmer than blood, fish and meat, but they are 

 also much less costly, and their presence in a fertilizer supposed to 

 be manufactured of the best materials is good evidence of fraud. 

 It is now possible to determine whether organic nitrogen of so poor 

 a quality is largely used in any fertilizer. 



The phosphoric acid of superphosphates is determined in three 

 forms, according to its solubility in various liquids, viz : soluble, 

 reverted and insoluble. 



Soluble phosxihoric acid is that which exists in fertilizers in a 

 form freely soluble in water. It is obtained by treating certain 

 phosphatic materials, such as bone and South Carolina rock, with 

 sulphuric acid (oil of vitriol.) 



In the chemical changes caused by the sulphuric acid, besides the 

 production of a soluble calcium phosphate, with perhaps some free 

 phosphoric acid, hydrated calcium sulphate (gypsum) is formed if 

 sufficient water be present, which is the same compound as land 

 plaster. The advantage of having the phosphoric acid of fertilizers 

 rendered soluble is not that it remains so in the soil, for it becomes 

 insoluble in water very shortly after application, but in the fact that 

 when the compounds of the soil change it back to an insoluble con- 

 dition it becomes deposited in particles so minute that they are 

 easily appropriated by the roots of plants. 



