714 EXPEKIMENT STATION EECOKD. 



those obtained by drying at 105° for 15 hours or so. A scale devised by the 

 author for rapid weighing is also illustrated and described. 



The determination of sugar in natural substances, C. Neuberg and M. 

 ISHiDA (Biochem. Ztschr., 37 {1911), No. 1-2, pp. 1^2-169; ahs. in Zentbl. 

 Physiol., 25 {1911), ISfo. 25, pp. 1199, 1200). — The polarimetric determination 

 of sugar in all cases is connected with a certain amount of error where optically 

 active substances (cleavage products), such as peptone, amido acids, amins, 

 etc., are present, as they are as a rule in human foodstuffs, but if the solution 

 containing them is first treated with mercuric acetate and then with phos- 

 photungstic acid interfering substances will be removed. The author first adds 

 a 50 per cent solution in water of mercuric acetate until no more precipitation 

 takes place, filters off the sediment, and then adds a 25 per cent aqueous 

 •solution of phosphotungstic acid until no more precipitation occurs. Care 

 must be taken not to add a large excess of mercuric acetate. No sugar is 

 retained in the precipitate, and that in the filtered fluid may be determined 

 by either the reduction or the polarimetric method. 



In regard to the composition of Fehling's solution as used at the present 

 time, O. LiJNiNG {Chem. Ztg., 36 {1912). No. 14, p. i2i ) .—Attention is drawn 

 to certain inaccuracies in several of the published directions for preparing 

 Fehling's solution. 



The amount of formic acid in honey, H. Fincke {Ztschr. Untersuch. Nahr. 

 n. Genusstntl., 23 {1912), No. 6, pp. 255-267; ais. in Jour. Soc. Chem^ Indus:, 31 

 {1912), No. S, p. ^02).— Continuing previous work (E. S. R., 26, p. 312), honey 

 was not always found to contain formic acid, but most of that examined con- 

 tained a volatile acid which reduced mercuric chlorid in amounts varying 

 from 0.003 to 0.02 per cent when calculated as formic acid. This acid was 

 present in both the free and combined state. Esters of formic acid could not 

 be detected. 



Attention is called to the fact that small quantities of formic acid are obtained 

 if invert sugar is distilled with steam, the quantity depending upon the acidity 

 of the solution. Sucrose when inverted with invertase does not yield formic acid 

 on distillation. Honeys free from formic acid were not found to yield any more 

 volatile acids than those derived from a corresponding amount of invert sugai". 



The analysis of vinegar, J. H. Paterson {Proc. Univ. Durham Phil. Soc, 

 Jf {1911-12), No. 3, pp. 144-146). — Normal vinegar contains acetic acid, and 

 small quantities of sodium tartrate and acetate. If the acetic acid is titrated 

 with a standard alkali solution, and the solution then titrated back with a 

 standard acid solution, using methyl orange as an indicator, the amount of acid 

 will be, therefore, a little in excess of that which would be equivalent to the free 

 acid found by the alkali titration. Vinegar adulterated with mineral acid will 

 not contain tartrates and acetates, but free acetic and tartaric acids will be 

 present. 



The method used is as follows: "A sample of the vinegar is boiled under a 

 reflux condenser with about i of its weight of animal charcoal (the charcoal is 

 previously treated with dilute hydrochloric acid to remove all carbonates, well 

 washed, and dried for some time at 110° C). The liquid is then filtered and the 

 interior of the condenser washed into the filtrate with some of the filtered 

 liquor. About 20 gm. of the filtrate are then weighed out and diluted to 100 cc, 

 with distilled water. Portions of 25 cc. are carefully titrated with tenth- 

 normal caustic potash, using phenolphthalein as indicator. The solution thus 

 obtained is diluted to a known volume (about 100 cc), and 6 drops of methyl 

 orange added. Decinormal sulphuric acid is then run in until a pink color with- 

 out any yellow shade is produced." 



