1919] AGRICULTURAL CHEMISTRY — AGROTECHNY. 505 



The estimation of sulphates in a concentrated electrolyte and the determi- 

 nation of sulphur in foods, V. K, Krieble and A. W. Mangum {Jour. Ainer. 

 Chem. Soc, 41 (1919), No. 9, pp. 1317-1328) .—As the outcome of a study of the 

 oxidation of food by sodium peroxid and the precipitation of sulphates as barium 

 sulphate in solutions containing large amounts of sodium chlorid, a modified 

 method Is described which is considered by the authors to be a decided improve- 

 ment both in the oxidation process and in the final estimation of sulphates in 

 materials such as food samples in which the sulphur content is low. 



Danger of the samples either exploding or taking fire during the oxidation is 

 avoided by mixing a suitable quantity of sodium carbonate with the second 

 addition of sodium peroxid in the fusion, and subsequently heating just one 

 side of the nickel crucible in order to start the oxidation locally and keep the 

 rest of the mixture in the crucible relatively cool. 



The technique of the precipitation of the sulphates as barium sulphate is as 

 follows : The solution of the oxidized material from 2 or 3 gm. of the original 

 sample is neutralized with concentrated hydrochloric acid, brought to a volume 

 of 350 cc. and heated to boiling on a hot plate. It is then removed from the 

 hot plate and the barium sulphate precipitated by adding slowly with a dropper 

 10 cc. of a 10 per cent barium chlorid solution. After standing for 48 hours 

 the mixture is evaporated to dryness on a hot plate, the precipitate dissolved 

 in a little water, and from 1 to 2 cc. of concentrated hydrochloric acid added. 

 After standing for 18 hours longer, the precipitate is collected in a Gooch cru- 

 cible, washed, dried, and ignited to constant weight. 



It is stated that the results obtained by this method will be high, and should 

 be corrected by a comparison of the amount of barium sulphate obtained by 

 making a determination on a solution of sodium or potassium sulphate of such 

 strength that the amount taken should give about the same amount of barium 

 sulphate as obtained from the food. 



The determination of lactose and of albuminoids in autoclaved milk and 

 in milk preserved by the addition of potassium dichromate, P. Defrance (Ann. 

 Falsif., 12 (1919), No. 125-126, pp. 78, 79).— The author refers to the conclusions 

 of Porcher and Bonis previously noted (E. S. R., 40, p. 613) that the polari- 

 metric determination of lactose in milk preserved with sodium bicarbonate is 

 unreliable, and states that he has arrived at the same conclusion in testing 

 milk preserved with potassium dichromate. In his opinion, however, the change 

 in rotatory power should be attributed to alterations in the casein rather than 

 in the lactose. 



On the estimation of sugar in blood, H. Maclean (Biochem. Jour., 13 (1919), 

 No. 2, pp. 135-I47, figs. 2 ) . — A method for the estimation of sugar in the blood is 

 described which is essentially a modification of a method previously introduced 

 by the author.* 



The principle of the method consists in sepai'ating the proteins by heat coagu- 

 lation in an acid saline solution and subsequently precipitating any remaining 

 traces of protein by the use of dialyzed iron. The sugar in an aliquot part of 

 the protein-free filtrate is estimated by boiling the liquid with an alkaline cop- 

 per solution containing potassium iodate and iodid and treating tlie solution 

 containing the reduced cuprous oxid in suspension with a slight excess of hydro- 

 chloric acid. This interacts with the potassium iodate and iodid, liberating 

 iodin equivalent to the amount of potassium iodate in the solution. The cuprous 

 oxid is changed to cuprous chlorid which immediately reacts with the free 

 iodin. The amount of sugar is calculated by a determination of the iodin used. 



' Jour. Physiol., 50 (1916), No. 3, pp. 168-182. 

 144402°— 19 2 



