1920] AGRICULTURAL CHEMISTRY AGROTECHNY. 313 



A spcctrophotoiiu'tric study of the " salt cnCcts " of i)liospIiates upon 

 the color of phenolsulfonphthaleiii salts and some biological applications, 



C. L. Bkightman, M. It. Meaciikm, and S. F. Ackee {Jour. Bad., 5 (11)20), yo. 

 2, pp. 169-180, figs. 2). — The iuitbors discuss the effect of the presence of cer- 

 tain salts upon the apparent values for H-ion concentration of sohitions as 

 determined by the hydrogen electrode and the sulfonphtbalein indicators, and 

 present data on the elTect of i)h<)sphate solulions upon the colorinietrie values 

 of pll. A table is given of the corrections in pll which nuist Ix^ added to the 

 observed colorinietrie pH'in order to give the true pit in solutions free from 

 phosphates and salt effects and having the same indicator transformation. 



" When measuring the limits of tolerance for hydrogen, or other ions, or 

 molecules by organisms, care should be taken to state the concentration of 

 chemicals and buffers used and possibly to free the published constants of these 

 ' salt effects'." 



Food inspection and analysis, A. E. Leach, revised and enlarged by A. L. 

 WiNTON {New York: John. Wilct/ d Sons, Inc., 1920, 4- ed., rev. and enl., pp. 

 XIX+1090, pis. 42, figs. 129).— In the fourth edition of this volume (E. S. II., 

 29, p. 2(>4) a large amoimt of new material has been added, including a final 

 chapter by G. L. Wend^ on the determination of acidity by the H-electrode. 

 The lists of references at the end of the chapters, a feature of the previous 

 editions, have been dropped and more attention has been given to footnote 

 references. 



The niicroscopical examination of flour, G. L. Keenan and M. A. Lyons 

 {U. S. Dept. Agr. Bui. 839 {1920). pp. 32).— The purpose of the investigation re- 

 ported in this bulletin was to determine the possibilities in the use of micro- 

 scopical methods for determining the offal content of flour of various com- 

 mercial grades. The technique employed was as follows : 



A 5-mg. portion of a composite sample of thoroughly mixed flour is carefully 

 weighed out on accurate balances and the weighed portion transferred with a 

 scalpel and camel's hair brush to the center of a microscopic .slide ruled across 

 the short diameter with lines about 0.5 nun. apart. About 3 or 4 drops of 

 chloral hydrate solution is added to the flour from a 1-mm. bore pipette and 

 the flour evenly distributed in the liquid by means of a preparation needle. 

 A .square cover glass is then applied and the slide carefully heated over the 

 alcohol flame until the starch grains are dissolved, after which the slide is 

 quickly transferred to the stage of the microscope, allowed to cool, and then 

 counted for bran particles and hairs, these being taken as constituting the offal. 



The investigation carried out by this method consisted of a preliminary 

 study to determine the limits of error in the method due to the personal 

 efjuation (including one analyst's variation in counting the same slides on 

 different days and the variation between two analysts counting the same slide 

 on the same day), daily variation due to the condition of light, slide variation 

 due to limits of accurate weigliing of the test portion of flour, and the varia- 

 tion in homogeneity of the bulk sample; an examination of the degree of purity 

 of the various mill stocks entering into the composition of commercial flours; 

 an examination of different commercial grades of flour; and an examination 

 of experimental series of flour the composition of which was definitely known. 



The prelinunary study indicated that the personal equation caus(>s slight 

 differences in the count, the average variation of two analysts for the same 

 sample being 20 for the bran particles and 18 for the count f>f hairs. Personal 

 variation due to error of counting was estimated at between VI and 17 points. 

 The other factors tested were not considered to have appreciable influence on 

 the count. 



