Oil AGRICULTURAL ANALYSIS 



It can not be recommended for the work which agricultural an- 

 alysts are usually called on to perform. 78 



100. Phosphoric Acid Soluble in Ammonium Citrate. There is 

 no other point connected with the determination of phosphoric 

 acid which has excited so much discussion and about which 

 there is such difference of opinion as the solubility of phosphates 

 in ammonium citrate. It was clearly established by Huston, in 

 1882, that the ammonium citrate, as used in fertilizer analysis, 

 would attack normal tricalcium phosphate as it exists in bones. 80 



In a raw bone, finely ground, containing 20.28 per cent, of phos- 

 phoric acid, the following quantities are found to be soluble in a 

 neutral ammonium citrate solution of 1 .09 specific gravity : 



Time of digestion, thirty minutes. 



Temperature 30 40 50 60 



Per cent. P 2 O 5 dissolved 2.76 4.01 3.39 5.88 



From this it appears that the quantity of acid dissolved in- 

 creases with the temperature of digestion with the exception 

 of the number obtained at 50. When the time of digestion is 

 increased there is also found a progressive increase in the amount 

 of acid passing into solution. At 40 for 45 minutes the per 

 cent, dissolved is 4.97, and 40 for one hour, 5.92. These early 

 determinations had the effect of calling attention to the thoroughly 

 empirical process which was in use, in many modified forms, by 

 agricultural chemists the world over for determining so-called 

 reverted phosphoric acid in fertilizers. Since the publication of 

 the paper above named many investigations have been undertaken 

 by Huston and others relating to this matter. 81 



The conditions of solution studied embraced the influence of 

 time, temperature, kind and quantity of material, and acidity and 



n Fresenius, Quantitative Analysis, Cohn's Translation of Sixth German 

 Edition, 1904, 1 : 450. 



80 Wiley, 32nd Annual Report of the Indiana State Board of 

 Agriculture, 1882 : 225. 



81 American Chemical Journal, 1884-5, 6 : i. 



Proceedings of the Convention of Agricultural Chemists, Atlanta 

 Meeting, 1884, Edited by C. W. Dabney, Secretary : 23, 28, 38, 45. 

 Division of Chemistry, Bulletin 7, 1885 : 18. 

 Division of Chemistry, Bulletin 28, 1890 : 171. 

 Division of Chemistry, Bulletin 31, 1891 : 99. 



