610 EXPERIMENT STATION RECORD. [Vol 40 



noted (E. S. R., 39, p. 507) gave results the average of which agreed with the 

 theoretical value very closely. Arsenious oxid is thought to be the more 

 reliable standard substance for practical use. 



Precautions in the preparation and use of standard iodin solutions are em- 

 phasized. 



The iodotannic reagent, D. E. Tsakaxotos and D. Dalmas (Bui. Soc Chim. 

 France, 4. ser., 28 (1918), No. 9, pp. 891-400; abs. in Jour. Chem. Soc. [Lon- 

 don], Ilk (1918), No. 674, II, p. 454; Analyst. 44 (1919), No. 514, pp. 85, 86).— 

 Tbe reagent described consists of a mixture of 1 cc. of N/10 iodin solution with 

 1 cc. of a 1 per cent tannin solution and is used to determine the alkalinity of 

 very dilute alkaline solutions. The technique is as follows : 



To the 2 cc. of freshly prepared reagent in a porcelain dish the alkaline 

 solution is added with stirring until a definite red color appears. The solution 

 is then added very gradually, and after each addition a drop of the mixture 

 is tested on starch paper. The end-point is reached when a blue color is no 

 longer formed on the test paper. By means of a table, the derivation of which 

 is described in detail, the alkalinity of the solution may be calculated, knowing 

 the volume used. 



It is said that exact results may be obtained by the use of this reagent with 

 alkaline solutions as dilute as N/10.000 to N/40,000. 



Estimation of silica and sand, F. J. Lloyd (Analyst, .}.} (1919), No. 514. pp. 

 27, 28). — A method of differentiating between soil sand and the natural silica of 

 feeding stuffs is described. This consists in determining the total siliceous 

 matter in the usual way by ashing the material and removing the other ash 

 constituents by digestion with hydrochloric acid, incinerating, and weighing the 

 residue or total silica. The residue is then digested wth 10 per cent sodium 

 hydroxid, washed with hydrochloric acid, filtered, and incinerated, the final 

 residue representing the sand as distinguished from natural silica. 



The author has found 9S per cent of the total siliceous matter of soil to remain 

 undissolved by successive acid and alkali treatment as above, while of the total 

 siliceous matter of straw 86 per cent is dissolved, indicating that the method 

 distinguishes fairly well between plant silica and the sand of soil. 



Estimation of silica and sand, B. Dyer (Aiialuxt. 44 (1919), No. 514, P- 

 28). — The author supplements the above note by describing a similar method 

 employed for a quantitative discrimination between sand and natural silica in 

 Indian rice bran. A 10 per cent solution of sodium carbonate was employed 

 Instead of sodium hydroxid. 



This method of treatment is said to dissolve 91 per cent of the natural silica 



of the rice husks and only about 5 per cent of sand. The percentage of sand is 



B — 09 A 

 then calculated from the following formula: Percentage of sand = - ■- n ' — 



v. 00 1 



where A equals total siliceous matter Insoluble in acid and B equals the siliceous 

 matter not redissolved by the treatment of sodium carbonate. 



The gravimetric and volumetric determination of zinc precipitated as zinc 

 mercury thiocyanate, G. S. Jamieson (Jour. Amcr. Chem. Soc, 40 (1918), No. 

 7, pp. 1086-1089). 



The determination of nitrous acid and nitrites, J. S. Laird and T. O. Simp- 

 son (Jour. Amer. Chem. Soc, 41 (1919), No. 4, PP- 524-581). — An investigation 

 of the volumetric methods described in the literature for the determination of 

 nitrous acid or nitrites is reported, and a modified method is described which is 

 said to give more satisfactory results. 



The method consists essentially of oxidation in acid solution with excess 

 permanganate, reduction of the excess permanganate with excess ferrous sul- 



