INSECTICIDES AND FUNGICIDES. 27 



a slight precipitate appears, then proceed as directed in the last two sentences 

 of Method II. 



(e) SODIUM-ACETATE-SOLUBLE ARSENIOUS OxiD.o PROVISIONAL. 

 (1) SOLUTIONS REQUIRED. 



Prepare the same solutions as are used in Method II for total arsenious 

 oxid, with the exception of the sodium potassium tartrate solution. 



(2) DETERMINATION. 



Proceed as described in the first three sentences of Method II for total arse- 

 nious oxid, except that a paper filter is used instead of asbestos. 



(f) WATER-SOLUBLE ARSENIOUS OXID.& PROVISIONAL. 



(1) SOLUTIONS REQUIRED. 



Prepare starch and standard iodin solutions as described under Method II. 



(2) DETERMINATION. 



Treat 1 gram of Paris green in a large flask with 1,000 cc of water (previously 

 boiled to expel carbon dioxid and then cooled to room temperature). Stopper 

 the flask and shake eight times each day for ten days. At the nd of this time 

 filter the solution through a dry filter. Treat 200 cc of this filtrate with sodium 

 bicarbonate and titrate with the iodin solution. 



(g) TOTAL COPPER OXID, METHOD I (ELECTROLYTIC). OFFICIAL. 



Pour the cuprous oxid (obtained in Method I, page 2G, for total arsenious 

 oxid by boiling the Paris green with sodium hydroxid) on the filter and wash 

 well with hot water, after an aliquot of the filtrate has been used for the deter- 

 mination of arsenious oxid. Then dissolve in hot dilute nitric acid and make 

 up to a volume of 250 cc. Use 50 to 100 cc of this solution for the electrolytic 

 determination of copper, as described on page 52, paragraph (2), under "VII. 

 General Methods for the Analysis of Foods and Feeding Stuffs." 



(h) TOTAL COPPER OXID,& METHOD II (THIOSULPHATE). OPTIONAL OFFICIAL. 



(1) SOLUTIONS REQUIRED. 



Standard thiosulphate solution. Dissolve 24.8 grams of the crystallized salt in 

 water and make up to 2 liters. Standardize this solution against chemically 

 pure copper foil dissolved in nitric acid by the method of analysis given in the 

 following paragraph : 



(2) DETERMINATION. 



Use an aliquot portion of the nitric-acid solution of copper oxid, employed in 

 Method I for total copper oxid. Make it alkaline with sodium carbonate, then 

 make slightly acid with acetic acid, dilute with water, and add about 3 or 4 

 grams of solid potassium iodid. When the potassium iodid is all dissolved by 



J. Amer. Chem. Soc., 1901, 23 (2) : 111. 

 6 Ibid., 1900, 22 (9) : 568. 



S7404 Bull. 10709 4 



