CHEMISTEY. 821 



" (4) Hot water extraction can not l)e used to extract solul^le arsenious oxid. 



"(5) A good method for determining copper in Paris and Scheele greens is the 

 volumetric method based on the titration of the iodin set free from potassium iodid 

 by a copper salt in acetic acid solution." 



Composition and analysis of London purple, J. K. Haywood 



{Jour. Amer. Cliem. Soc.,22 {1900), No. l'2,pp. 800-809). -The author 

 finds London purple to consist of calcium arsenite, calcium arsenate, 

 and an organic dye. 



^After a trial of several methods of analysis the following was found 

 very satisfactory in determining the arsenic in London purple: Two 

 grams of substance is dissolved in 80 cc. water, 20 cc. hydrochloric 

 acid added at 60 or 70^, and the whole filtered and washed to a volume 

 of 300 cc. An aliquot of 100 cc. is treated with sodium carbonate in 

 excess and made up to 500 cc. , using a few drops of ether to destroy 

 bubbles; 250 cc. of this solution is filtered, starch solution added and 

 a standard iodin solution until the blue color appears. The residt 

 represents the arsenious oxid as such in 50 cc. of the original solution 

 or in i gm. substance. 



To determine the total amount of arsenic 50 cc. of the original solu- 

 tion, representing ^ gm, of substance, is heated in a water bath to 80^, 

 after which 50 cc. of hydrochloric acid and 3 gm. of potassium iodid are 

 added. After standing 15 minutes the arsenate is reduced to arsenite 

 by the action of the potassium iodid, the iodin being set free. The 

 solution is then rinsed out in a large beaker and tenth-normal sodium 

 thiosulphate added, drop by drop, to get rid of the iodin. On account 

 of the dark color the end point is' hard to read without practice. 

 Tests are made from time to time with a drop of the solution on starch 

 paste. After the operation is completed the solution is immediatel}' 

 made alkaline with solid sodium carbonate, again made slightly acid 

 with hydrochloric acid and finally alkaline with sodium bicarbonate. 

 Starch paste is now added and deci-normal iodin until the blue color 

 appears. The figure thus obtained gives the total amount of arsenic 

 present as arsenious oxid. 



Methods are also given for determining the calcium oxid and the 

 solul)le arsenious and arsenic oxids in London purple. 



Detection of coal-tar dyes in fruit products, A. L. Winton {Jour. 

 Amer. Chem. Sog.,22 {1900), No. 9, pp. 582-588).— The author mentions 

 the increased use of coal-tar colors in the preparation of fruit jellies 

 (frequently artificial), fruit preserves, soda-water sirups, etc. In the 

 absence of special methods for detecting these, he has adapted a num- 

 ber of methods originally devised for wines. Working descriptions 

 are given for Arata's wool test, the amyl alcohol tests (alkaline solution 

 and acid solution), Girard's tests for acid fuchsin, and Cazeneuve's 

 method, together with precautions which have been learned by 

 experience. 



