114 EXPERIMENT STATION RECORD. [Vol. 40 



Volumetric determination of reducing 1 sugars, W. B. Clark (Jour. Amer. 

 Chem. Soc, J,0 (1918), No. 12, pp. 1159-1112, fig. 1).— The method, contributed 

 from the Bureau of Plant Industry. U. S. Department of Agriculture, is a sim- 

 plification of Scales's method, previously noted (E. S. R., 34, p. Gil), for titrating 

 the reduced copper without removing it from the residual copper solution. The 

 entire process is carried out in a single vessel with practical exclusion of the 

 air from the time the reduction takes place until after the oxidation by the 

 iodin. Concentrations of the solutions used and a definite method of procedure 

 are described for quantities of reducing sugars up to 75 mg., and principles are 

 pointed out for adapting the process to larger quantities of such sugars. 



The accuracy of the method is said to be such that with care the results of 

 duplicate determinations should not differ by more than 0.2. r > mg. of reducing 

 sugar. The ratio of reducing sugar to copper is nearly constant, the greatest 

 variation occurring in low values. Instead of using tallies it is advised that each 

 observer standardize his own procedure and then determine the ratio for that 

 procedure. 



Determination of aldehyde sugars by iodin in an alkaline medium: Appli- 

 cations, H. ('or. in and O. Lievin (Hul. Soc. Chim. France, -i. scr., tS-24 (1918), 

 No. 9, pp. 408-405 ; ab8. In ./our. Soc. Chem. Indus., 31 {1918), A o. 98, p. 7 ',-', \ i. — 

 Suggestions are given for slight modifications in the Bougault method for the 

 determination Of aldehyde sugars by means of iodin (E. s. K.. :\~, p. 714 ). and 

 comparative results are reported on tubercles, roots, and leaves obtained by the 

 use of this method and the polarimetric method. The results in general were 

 concordant, although w ith leaves the results are considered uncertain and always 

 too high. 



A method for the determination of starch. W. S. Long (Trims. Kans. Acad. 

 Set, 28 {1916- 17), pp. 179-174).— The method is described as follows: 



To 5 cc. of starch solution in a 100 CC flash are added 5 cc. of a o per cent 



N 

 solution of potassium iodid and '20 cc. of * solution of iodin in a 5 per cent 



otHJ 



potassium iodid solution. The flask is stoppered, shaken, ami allowed to stand 

 over night. The precipitated starch iodid is then tillered and washed thor- 

 oughly with a 5 per cent potassium Iodid solution. The filtrate and washings 



N 

 are titrated with ' sodium thiosulphate solution, using starch solution as 

 ouU 



indicator. 



The method is thoughl to he sufficiently accurate to be applicable to the de- 

 termination of starch when occurring in small amounts, as in various food 

 products. 



The determination of pentosans, II. D. S 1 1 i mikrgen (Chem. Weekbl., 15 

 (1918), No. 25, pp. 784-808).- -This is a review and critical discussion of various 

 methods for determining pentosans. An extensive bibliography is given. 



A study of some biochemical color tests. — I, The thiophone test for lactic 

 acid. A color test for aldehydes, \Y. R. Feasor {Biochem. Jour., 12 (191S), 

 No. 3, pp. 179—188). — The author proposes the term " hydrocnic " for biochemical 

 color reactions, the products of which are decolorized by the addition of small 

 quantities of water, and describes the thiophene test for lactic acid as a typi- 

 cal hydrocnic reaction. The reaction is due to the production from lactic acid 

 of formaldehyde and acelaldehyde, which react with the thiophene in tin- pres- 

 ence of excess of sulphuric acid to give a cherry-red color. On the basis of 

 this reaction a new color test for aldehydes is described as follows: 



Two drops of a 0.2 per cent alcoholic solution of thiophene are added to 

 5 cc. of concentrated sulphuric acid (free from nitrous and nitric contamina- 

 tions) and mixed. 1. a drop of a weak solution of an aldehyde be added, a 



