AGRICULTURAL CHEMISTRY — AGROTECHNY. 311 



nonsugar wliioli. on the average, is l.Sl. By inserting the valnes of O and g 

 the equation becomes riHlueed to the more convenient form: N = 1.000 (D — D') 

 2.232." 



An electrically controlled constant temperature water bath for the 

 immersion refractometer, H. C. Gore (f/. »S'. Dept. Agr., Bur. Chem. Circ. 72, 

 pp. 2, figs. 2). — In this apparatus the inflow of cooling water is regulated 

 automatically by a telegraph sounder pressing upon a rubber outflow tube 

 which controls the admittance of water to the water bath. The thermostat 

 proper consists of a long glass tube filled with mercury, closed at one end and 

 bent into a flat rectangular coil which is fastened to a perforated brass plate 

 resting on feet on the bottom of the water bath. At the open end of the tube 

 is attached a device in which electrical connection is made between the mercury 

 and platinum wires sealed in the tube. The platinum wires connect with the 

 relay and this, in turn, communicates with the sounder mentioned above. 



Estimation of formic acid in foods, H. Fincke (Ztschr. Untersuch. Nahr. u. 

 Genussnitl, 21 {Wit), No. 1, pp. 1-15; abs. in Analyst, 36 (1011), No. .',20, pp. 

 103, lO'i). — The Auerbach and Pliiddemann method,** which utilizes mercuric 

 chlorid for estimating the formic acid, was iuA-estigated by the author, who 

 describes procedures for removing the substances, which, when present, inter- 

 fere with the accuracy of the method. He finds it convenient whei*e numerous 

 estimations are to be made to use the volumetric method, first neutralizing the 

 formic acid solution, then heating it for 2 hours on the boiling water bath with 

 a known quantity of standard mercuric chlorid solution (58.87 gm. of mercuric 

 chlorid and 15 gm. of sodium chlorid per liter), and titrating the excess of 

 mercuric chlorid with jjotassium iodid solution. 



For occasional determinations the gravimetric method may be employed, 

 thereby avoiding the preparation of standard solutions. In this case the 

 formic acid solution is boiled with sodium acetate and an excess of mercuric 

 chlorid under a reflux condenser. The precipitate of mercurous chlorid is 

 weighed after having been successively washed with warm water, alcohol, and 

 ether, and dried at 100° C. For foods it is necessary to acidify the sample 

 with tartaric acid and to distill with steam until a distillate of at least 1,500 

 cc. has been obtained. ?>Iineral acids are not recommended, as they caramelize 

 the foods and volatile products are given off which reduce the mercuric 

 chlorid. 



When acetaldehyde or formaldehyde is present it becomes necessary to 

 interpose a flask containing water and calcium carbonate between the distilling 

 flask and the condenser, the flask being heated during the operation. The 

 formic acid is retained in the flask containing the calcium carbonate, and the 

 calcium carbonate is filtered off and the acid determined in the filtrate. 



When sulphurous acid is present the filtrate from the calcium carbonate 

 flask, or the distillate itself, is neutralize<l and concentrated to a bulk of 100 cc. 

 The solution thus obtained is treated with sodium hydroxid and peroxid, and 

 after standing for 4 hours the excess of peroxid is removed by freshly precipi- 

 tated mercuric oxid and sodium acetate. After standing for 30 minutes the 

 formic acid is estimated in the filti'ate. Salicylic acid yields an insoluble pre- 

 cipitate with mercuric chlorid and sodium acetate, but this precipitation can be 

 prevented by having some sodium chlorid present. 



The relation of the nitrog'enous constituents in milk and cream, H. Hoft 

 {Arb. Vers. Stat. Mollcw. Kiel, 1909, No. 6, pp. 7-11). — The author points out 

 that the unexplained nitrogen i-esidue which remains in milk after all other 



"Arb. K. Gsndtsamt, 30 (1909), pp. 178-194. 



