1917] AGRTCULTUKAL CHEMTSTEY — AGEOTECHNY. 713 



f erred to a 400-cc. beaker containing an excess of standard fiftti-norraal 

 potassiinu permanganate, and diluted to 250 cc. The beaker is then placed 

 on a steam bath for about 15 minutes and acidulated with 10 (jc. of 1:1 sul- 

 phuric acid, the excess permanganate is removed with standard fifth-normal 

 oxalic acid, and the clear solution retitrated with standard potassium perman- 

 ganate solution. 



For determining " water-soluble " potash 10 gm. of the material is weighed 

 into a 600-cc. beaker and boiled with 250 cc. of water for 30 minutes. It is 

 then transferred to a 500-cc. flask, cooled to room temperature, and made to the 

 mark. After shaking well, a portion of the solution is filtered through a dry 

 paper and 50 cc. of the filtrate placed in a platinum or porcelain dish. The 

 procedure is then carried out as given above. 



Directions for preparing the cobalt-nitrite solution and calculation of the po- 

 tassium oxid factor are given. 



The method has been used for some time and has yielded most satisfactory 

 results on total potash when checked against the J. Lawrence Smith method, 

 and on water-soluble potash when checked against the official method. 



The solubility of calcium phosphates in citric acid, A. A. Ramsay (Jour. 

 Agr. Set. [England], 8 {1911), No. 3, pp. 277-298) .—The results of the study 

 reported show that the materials sold as " phosphate of lime " and " Calcii 

 Phosphas B. P." are not tricalcium phosphate, but mixtures of di- and trical- 

 cium phosphates. By adding disodium phosphate to ammoniacal calcium chlorid 

 a mixture of di- and tricalcium phosphate and calcium hydrate is obtained. 

 Bone ash dissolved in hydrochloric acid and precipitated with ammonia (as In 

 the directions for preparing tricalcium phosphate according to the British 

 Pharmacopoeia) also yields a mixture of di- and tricalcium phosphate and 

 calcium hydrate. When three equivalents of calcium oxid act on one equiv- 

 alent of phosphoric acid and the resulting precipitate is immediately removed 

 pure tricalcium phosphate is obtained. When two equivalents of calcium oxid 

 react on one equivalent of phosphoric acid the product obtained is not dical- 

 cium phosphate, but a mixture of di- and tricalcium phosphate. 



Of the total phosphoric acid of pure tricalcium phosphate 91 per cent is 

 soluble in 2 per cent citric acid solution in 30 minutes, as determined by the 

 method adopted for the determination of " citrate-soluble " phosphoric acid. 

 By addition of calcium carbonate to a pure tricalcium phosphate the " citrate 

 solubility " of the phosphoric acid is reduced from 91 to 84 per cent. It is 

 noted that the 2 per cent citric acid solution is rather a solvent for lime than 

 for phosphoric acid. 



" Since tricalcic phosphate and dicalcic phosphate are' both soluble in the 

 prescribed 2 per cent citric acid solution the statement that dicalcic phosphate 

 can be differentiated from tricalcic phosphate by means of the selective action 

 of this solvent is untenable. It follows that the manurial value of phosphates 

 can not be determined by a 2 per cent citric acid solvent in the method pre- 

 scribed, and it therefore is a matter for consideration whether or not the 

 further use of this method should be continued." 



See also previous notes of Hopkins (E. S. R., 87, p. 214) and Jatindra Nath 

 Sen (E. S. R., 37, p. 615). 



A method for the destruction of organic matter in animal and vegetable 

 materials for the determination of arsenic and the examination of the ash, 

 A Gautieb and P. Clausmann {Compt. Rend. Acad. Scl. [Paris], 165 (1917), 

 No. 1, pp. 11-16). — The procedure, which consists essentially of heating the dry, 

 finely pulverized material with calcium oxid, is described in detail. The method 

 can also be used for preparing material for the determination of boric, phos- 

 phoric, and silicic acids, fluorin, nickel, silver, and copper. The procedure rec- 



