26 



The Avery hydrogen-peroxid method for determining sulphur in 

 sulphur dips, etc., was adopted as provisional: 



LIME-SULPHUR DIPS AND LIME-SULPHUR-SALT MIXTURE (PROVISIONAL). 



TOTAL SULPHUR. 



SOLUTIONS REQUIRED. 



A saturated potassium hydroxid solution or a solution of caustic soda containing 100 

 grams to 100 cc of water. A 10 per cent barium chlorid solution. An approximately 3 per 

 cent solution of hydrogen peroxid free from sulphates; if it contains sulphates add freshly 

 precipitated barium carbonate and shake occasionally for several hours, then filter and use 

 the clear solution. 



METHOD. 



Measure off 10 cc of the clear sample in a 100-cc measuring flask and fill to the mark. Use 

 aliquot portions of 10 cc of this for analysis. Treat this aliquot with 3 cc of the caustic 

 potash or soda solution, following this by 50 cc of hydrogervperoxid free of sulphates. Heat 

 on the steam bath for just one-half hour and then acidify with hydrochloric acid, precipitate 

 with barium chlorid in the ordinary manner in boiling solution, and finally weigh as barium 

 sulphate. 



Twenty-second Convention. 1905, Bui. 99, Cir. 26. 



Methods I and IV, modifications of the Avery-Beans of determining 

 total arsenic in paris green were adopted as optional official methods : 



Method I. A weighed sample of the green was boiled with sodium acetate as in the 

 determination of soluble arsenic by his (Avery's) method, the mixture filtered through 

 asbestos, the soluble arsenic determined in the filtrate and the residue of the asbestos dis- 

 solved in dilute hydrochloric acid and titrated according to the Avery-Beans method 

 (Method II, provisional). 



Method IV. Take 0.4 gram of the finely ground green and boil with 25 cc of sodium acetate 

 (containing 12 grams) for 10 minutes. Then add concentrated hydrochloric acid a drop at 

 a time until solution is effected (about 10 cc of the acid will be necessary) . Add concentrated 

 sodium carbonate solution a drop at a time until a slight precipitate appears, then add a 

 solution containing 2 to 3 grams of sodium potassium tartrate and finally sodium bicarbonate 

 in excess. Titrate with iodin in the usual manner (Haywood's modification) 



The thiosulphate method was adopted as an optional official method, 

 using N/20 instead of N/10 thiosulphate solution. 



TOTAL COPPER OXID (OPTIONAL OFFICIAL). 

 SOLUTIONS REQUIRED. 



A standard twentieth-normal solution of sodium thiosulphate is prepared by dissolving 

 24.8 grams of the crystallized salt in 2 liters of water. This solution is standardized againsi 

 C. P. copper foil dissolved in nitric acid by the method of analysis given in the following 

 paragraph. 



METHOD. 



An aliquot portion of the nitric acid solution of copper oxid, used in Method I for total cop- 

 per oxid, is made alkaline with sodium carbonate, then made slightly acid with acetic acid, 

 diluted with water, and a considerable quantity of solid potassium iodid added, about 2 or 3 

 grams. When it is all dissolved by shaking, the free iodin is titrated with the twentieth- 

 normal thiosulphate, using starch as indicator. 



