l:r.'0| AGRICULTITRAI. C'lIKMIS'TRY^AGROTKC^HNY. 113 



is rccoiiimcndi'd. Tliis cliiiiijie is ronsidcred iiocessury if Sixliuni is present ii» 

 any quiiiility on account of tiie occlu.son of sodium percldorate witii tlie iM)tiiH- 

 siuiii percldoiate. If the amount of sodium is small, the use of u saturated 

 solution of potassium iKTchloiate for the initial extraction is considered sale. 



The use of solutions of aninioninm citrate for the estimation of reverted 

 calcium phaspliate, C. H. Uokinson (Mkhiijun Sta. Tech. Bui. Jf6 (I'Jl'J), pp. 

 ^^y).— This bulletin consists of a discussion of the standardization of the am-^ 

 nionium citrate solutions used in the estimation of reverted calcium phosphate. 

 The discussion is centered about the following points: (1) The i)n'paration of 

 aniiiionium citrate solutions having a definite reaction or composition; (2) the 

 n-lalion hi'tween comiiosition and reaction; and (3) the relation l)et\veen the 

 reaction of the reagent and its solvent action on calcium phosphates both pure 

 and in connnercial fertilizers. 



Tli(> comparative merits of the use of truly neutral solutions of ammonium 

 citrate, solutions of triammonium citrate, and solutions of empirical composi- 

 tion are discussed fn)m tiie literature on the subject and from experimental 

 •lata obtained by the author. By an application to the method of Kastman and 

 Hildebrand {K. S. II.. 32, p. S()4) of the standards prepared from potassiiun 

 hydrogen phosi)hate and sodimn hydroxid according to Clark and Lubs 

 (E. S. K., 37, p. 50G) with phenol red ax an indicator, he has found it possible 

 to obtain accurate neutral solutions of anunonium citrate. The composition of 

 a neutral solution of anunonium citrate standardized by this method has 

 been found to be 45.33 gm. Nils and 172 gm. CoHsOt per liter. The ratio of 

 Nil.-, to CJKO7 is 1 : 3.794 and the .sitecific gravity of the solution 1.09 at 20° O. 



Analytical data on the relation between the reaction of the reagent and its 

 solvent action on calcium phosphates are presented from which tlie following 

 conclusions are drawn: 



"With commercial fertilizers the reaction of acid or neutral citrate solutions 

 does not chynge during the determination but the alkalinity of alkaline solutions 

 is decreased. With mixtures of pure calcium phosphates and calcium sulphate 

 tlie reverse is true, i. e., acid and neutral solutions become more alkaline while 

 alkaline ones do not change. 



" With citrate solutions ranging in reaction from pH G.G to 7.8, the magnitude 

 of the variation in the results of the analysis of calcium pliosphate is usually 

 .small. There i.s, however, a distinct decrea.se in the solubility of both di- and 

 tri-calcium phosphate with an increase in alkalinity. Trecipitated tricalcium 

 phosphate is nmch more readily soluble in ammonium citrate solution than is raw 

 rock phosphate." 



In conclusion the author recommends the retention of the neutral solution 

 of anunonium citrate as the reagent to be employed in the estimation of 

 reverted calcium phosphate, but the replacement of the usual methods for 

 preparing the solution by more accurate ones such as the one described in this 

 study. 



A bibliography of 54 titles is appended. 



A rapid method for the identification of bacteria fermenting carbo- 

 hydrates, J. Bkonfenbrenner and M. J. Schlesinger (.Amer. Jour. Pub. Health, 

 8 {i;H8), No. 12, pp. 922, 923).— The method, which was devised to facilitate 

 the bacteriological examination of feces in studies of cases of food poisoning, 

 consists essentially in planting each of the suspected colonies into an agar 

 drop, thus permitting a comparatively large number of bacteria to grow in a 

 circumscribed area and thereby hastening the reaction. The lactose agar c(m- 

 talidng a suitable (piaiitity of indicator, preferably the CU indicator, is deposited 

 while. hot in drops from sterile pipettes on the inner surface of the bottom of 



I 



