24 



to read the end reaction. (Sometimes the solution gets dark toward the end of the titration. 

 This must not be confused with the final dark blue color given by the iodin and starch.) 



From the number of cubic centimeters of iodin solution used and the weight of arseni- 

 ous oxid taken, the value of each cubic centimeter of iodin in arsenious oxid can be 

 determined. 



Method (Smith modified by Haywood). Two grams of pans green are weighed out and 

 transferred to a 250 cc flask and about 100 cc of water and 2 grams of sodium hydrate added- 

 This solution is boiled for 5 to 10 minutes, or until all of the green particles have changed 

 to red cuprous oxid. It is then cooled to room temperature and the volume made to 

 250 cc. The well-shaken liquid is filtered through a dry filter and 50 cc taken for analysis. 

 The analysis is carried out from this point forward the same as when we standardize the 

 iodin solution. (In duplicate.) 



Method II. (Provisional.) a 



Solutions. The solutions required are the same as above, with the addition of a solution 

 containing 2 to 3 grams of sodium potassium tartrate in 50 cc of water. 



Method (Avery-Beans). Sample the paris green (as one would an ore for assaying) 

 down to about 1 gram. Pulverize this small sample in an agate mortar and weigh out 

 0.2 to 0.3 gram in a beaker of, say, 300 cc capacity. Add 25 cc of water, and to the green 

 suspended in the water add, with constant stirring, concentrated hydrochloric acid till 

 solution is just effected. Six drops are usually sufficient. Now add to the acid solution 

 sodium carbonate solution till a slight permanent precipitate is formed. Dissolve this 

 precipitate by adding 2 to 3 grams of sodium potassium tartrate in solution. Now dilute to 

 about 200 cc, add solid sodium bicarbonate and starch solution, and titrate with iodin in 

 the usual way. (In duplicate.) 



Nineteenth Convention, 1902, Bui. 73. 



Method I, provisional, for the determination of total arsenious oxid 

 in paris green, was recommended for adoption as an official method. 

 [Confirmed in 1903.] 



Twenty -first Convention, 1904, Bui. 90, Cir. 20. 



Use N/20 instead of N/10 iodin in titration of arsenic, i. e., Method I, 

 iodin solution, line 3, for " 1 liter" read " 2 liters." 



The electrolytic method was adopted as official for the determina- 

 tion of copper in paris green and copper carbonate. 



This method is slightly modified as follows when used for this 

 determination : 



TOTAL COPPER OXID, METHOD I (OFFICIAL). 



METHOD. 



The cuprous oxid obtained in Method I for total arsenious oxid, by boiling the paris 

 green with sodium hydroxid, is poured on the filter and well washed with hot water, after 

 an aliquot portion of the filtrate has been taken for the determination of arsenious oxid. 

 It is then dissolved in hot dilute nitric acid and made up to a volume of 250 cc. Fifty 

 to 100 cc of this solution is used for the electrolytic determination of copper, as described 

 on page 37, paragraph 2-b of Bulletin 46 (revised), Bureau of Chemistry, U. S. Department 

 of Agriculture. 



a This method should be dropped, as it has been adopted in modified form as an optional 

 official method (1905). 



