804 EXPERIMENT STATION RECORD. [Vol.43 



The determination of small quantities of phosphoric acid as barium 

 phosphomolybdate in the presence and absence of phosphorus in orajanic 

 combination, S. Posternak (Bui. Soc. CJmn. France, 4- -ler., 27 {1920), Xo. 12. 

 pp. 507-518). — The author states that it is possible to determine with sn-eat 

 accuracy as small amounts as 0.05 nig. of phosphorus as barium phospho- 

 molybdate by precipitating with the corresponding ammonium salt in a medium 

 exclusively sulphuric or nitric. 



In the first case, which applies to all determinations of phosphorus in the 

 absence of organic matter, a mixture of 10 cc. of the solution containing the 

 phosphorus, 10 cc. of 20 per cent ammonium sulphate, and 1 cc. of concentrated 

 sulphuric acid is heated to boiling in a 100 cc. beaker of Bohemian glass, after 

 which 5 or 10 cc. of a 10 per cent solution of ammonium molybdate is added 

 and the mixture allowed to stand for 15 minutes. The precipitate is filtered, 

 washed five times with a 5 per cent solution of ammonium nitrate, dissolved 

 in a little ammonia, reprecipitated with a 10 per cent solution of barium 

 chlorid, filtered, washed with a little water, dried, and heated for a few 

 minutes at red heat. The precipitate thus obtained corresponds to the formula 

 4Ba27 [PO4 (MoO0i2]2+Ba»SO4 (Mo 04)8 and the factor by which the weight of 

 the precipitate must be multiplied to obtain the weight of phosphorus is 0.00739. 



In the second case, whicli applies especially to the determination of inorganic 

 phosphates in the presence of organic compounds of phosphorus, a mixture of 

 20 cc. of the phosphorus-containing solution, 10 cc. of 20 per cent ammonium 

 nitrate, and 10 cc. of the molybdic reagent is allowed to stand, with occasional 

 shaking, at a temperature of from 12 to 15° C. for two hours, after which the 

 precipitate is filtered and treated as above. The resulting precipitate is said 

 to have the formula SBazi [PO4 (Mo Oi),2]2+Ba4 (Mo O*), and the factor is 

 0.007S6. 



The technique of the determination of phosphoric acid as barium phos- 

 phomolybdate, S. PosTEENAK (Bill. Soc. CMm. France, 4. ser., 27 (1920), No. 

 IS, pp. 56.'f-568). — This article describes in detail the technique of the method 

 noted above and calls attention to possible sources of error. 



Determination of cyanamid and dicyandiamid in calcium cyanamid, Mab- 

 QUEYBOL, P. LoBiETTE, and L. Desvebgnes {Ann. Chim. Analyt., 2. ser., 2 {1920), 

 No. 6, pp. 164-167). — The authors present evidence, both from the literature 

 and from laboratory investigation of different methods, indicating that the 

 original methods of Caro for determining cyanamid and dicyandiamid in 

 calcium cyanamid (E. S. R., 2.5, p. 24) are more accurate than later modifica- 

 tions of other authors. In particular, volumetric methods, such as that of 

 Kappen (E, S. R., 21, p. 419), based upon the determination of the silver in 

 silver cyanamid and dicyandiamid are considered to be inexact. 



Degree of alkalinity necessary for the phloroglucin test for formalde- 

 hyde, P. J. Hanzlik {Jour. Biol. Cheni., 42 {1920), No. 3, pp. 4ii--i 13). —The 

 author presents evidence indicating that the phloroglucin test for free formalde- 

 hyde requires for a minimal positive reaction a rather high degree of alkalinity 

 (pH=12.13), the equivalent of the alkalinity of a 0.04 per cent or n/100 sodium 

 hydroxid solution, and for an optimal reaction an n/10 hydroxid or carbonate 

 (pH=13). The neglect of this factor and the use of impure phloroglucin are 

 considered to be the causes of frequent failures in the use of this reagent. 



Determination of caflfein in mixtures of coffee and coffee substitutes and 

 in decaffeinated coffee, E. Vautiek {Ann. CMm. Analyt., 2. ser., 2 {1920), No. 

 6, pp. 168-172). — The method for determining caffein in coffee previously de- 

 scribed (E. S. R., 40, p. 115) is considered to give too high results with sam- 

 ples of low caffein content such as the so-called decaiTeinated coffee and mix- 



