AGRICULTURAL CPIEMTSTRY. 209 



results, which were much lower than Ihose yielded by the Schenko modification. 

 The latter also gave decidedly higher r(>sults than the citrate method on super-, 

 jihosphates. The volumetric methods, of which the liteniture is critically 

 reviewed, include the lead method of Schwarz, the alum metliod of Fleischer, the 

 bisnmth-nitrate method of Chancel, the silver method of Perrot, the uranium 

 method of Le Conte and others, the molybdic method, and various titration 

 methods. 



The determination of the organic nitrogen in sewage by the Kjeldahl proc- 

 ess. II, Studies of direct nesslerization, !>. Whipple {Tcclinol. Quart.. 20 

 {lixn), ?t'o. 2, pp. J 62-169 ).^-The K.1eldahl method, as used for the determina- 

 tion of organic nitrogen in sewage in the Massachusetts Institute of Technology, 

 is described and tests of possible sources of erx'or are reported. 



One of the i»rincipal difficulties encountered in the use of the method is the 

 turbidity of the digestate. Under ordinary conditions there is not sufficient cal- 

 cium present in sewage to cause trouble from turbidity, but even small amounts 

 of magnesium will render correct reading impossible. The latter, however, can 

 be easily removed by adding an excess of li per cent sodium hydroxid. The 

 digestate is then filtered and directly nesslerized. 



The analysis of silicate and carbonate rocks, W. P. Hillebkand (U. S. Geol. 

 Sitrrcij Bid. Sd-l. pp. 200, fli/.s. 2.'/). — This is a revision of Bulletin 176 of the 

 (Jeological Survey (E. S. R., 12, p. 1006). The methods described are in the 

 main those which have been perfected in the laboratory of the sux'vey, but are 

 not restricted to such methods. "A number of alternative ones are given which 

 are known or believed to be good, in order that those who may wish to use this 

 treatise as a practical guide shall have some choice of selection in case the 

 expensive apparatus or complicated arrangements sometimes preferred are not 

 available." 



Precipitation and alkalimetric determination of silicon fluorid in the 

 analysis of silicates, A. IIileman (Ztsclir. Anorgan. Vlicni., 51 (1906), pp. 

 15,S-17(): uhs. ill Bui. Soc. Chiiii. France, .'/. ser., 2 (1907), Ko. 11, p. 681). — From 

 comparative tests of various methods which have been proposed for this pur- 

 pose, the author concludes that the Peufleld and Bullnheimer methods give 

 identical results and are more i-eliable than the other methods tested. 



Determination of calcium carbonate in marl, M. J. van't Kruijs (Chem. 

 Weekhl., Jf (1901), pp. 29-32; abs. in Jour. Chem. Soc. [London], 92 (1907), No. 

 533. II, pp. 197, 198). — In the method reconnnended the sample of marl is reduced 

 to a fine state of division by repeated grinding with successive small (luantities 

 of water, the fine powder in suspension being transferred to a Scheibler appara- 

 tus, and the carbon dioxid set free by addition of 30 per cent acetic acid. The 

 reaction is considered complete in 1^ to li hours. 



On the flocculation of clay emulsions, II. Hermann (Ztsclir. Anorgan. Chem., 

 53 (1907). Xo. //, pp. .'il3-.'fl8, figs. J). — Observations on the effect of stirring and 

 of the addition of different amovmts of potassium nitrate are recorded. 



A formaldehyde color test for proteids, I, S. F. Agree (Amer. Chem. Jour., 

 37 (1907), Xo. G, pp. 60.'f-619). — A preliminary account of a study of the impor- 

 tance' of formaldehyde as a reagent for the detection of protein. 



The author was led to undertake the work by the fact that when a small 

 amount of casein or lactalbumin is mixed with a dilute formaldeh.vde solution 

 and a small amoimt of concentrated sulphuric acid is added a violet zone is 

 formed between the sulphuric acid and the solution. All of the proteids which 

 the author has yet studied give the violet color when tested by this method, 

 whereas, " in general, such substances as simple organic acids, sugars, alcohols, 

 esters, amids, phenols, urazoles, semicarbazids, amino acids, polypeptids, and 



