Frorn the number of cubic centimeters of iodin solution used and the weight 

 of arsenious oxid taken, the value of each cubic centimeter of iodin in terms of 

 arsenious oxid can be determined. 



METHOD. 



Two grams of paris green are weighed out ancj transferred to a 250-cc flask 

 and about 100 cc of water and 2 grams of sodium hydroxid added. This mixture 

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

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

 up to 250 cc. The well-shaken liquid is filtered through a dry filter and 50-cc 

 portions taken for analysis. The analysis is carried out from this point for- 

 ward the same as when standardizing the iodin solution. 



TOTAL ARSENIOUS OXID, METHOD .II (PROVISIONAL). 1 



SOLUTIONS REQUIRED. 



A standard, approximately twentieth-normal, solution of iodin is made as 

 follows: Dissolve 12.7 grams of powdered iodin in 250 cc of water to which has 

 been added 25 grams of potassium iodid, and make up to 2,000 cc. To stand- 

 ardize this solution weigh out 1 gram of dry C. P. arsenious oxid, transfer to 

 a 250-cc flask, and dissolve by boiling about 20 minutes with 5 grams of 

 sodium bicarbonate and about 100 cc of water; cool; add hydrochloric acid till 

 acid, and sodium bicarbonate again until alkaline; make to the mark and take 

 aliquots of 50 cc for standardizing. 



A solution of sodium acetate containing 12.5 grams of the crystallized salt in 

 each 25 cc. 



A solution containing 2 to 3 grams of sodium potassium tartrate dissolved in 

 each 50 cc. 



A starch solution. 



METHOD. 



A gram of paris green is weighed out and transferred to a 100-cc flask, where 

 it is boiled for 5 minutes with 25 cc of a solution of sodium acetate containing 

 12.5 grams of the crystallized salt. It is then made to the mark, shaken, and 

 passed through a dry asbestos gooch filter. An aliquot portion of this filtrate 

 is used to determine the soluble arsenious oxid. The residue on the filter is 

 transferred to a brakcr, and, after being beaten up with a little water, dissolved 

 in hydrochloric acid by adding the concentrated acid a drop at a time. The 

 whole is now transferred to the 100-cc flask and aliquot portions of 20 to 40 cc 

 each taken for analysis. To each of these aliquots is added concentrated sodium 

 carbonate solution a drop at a time until a slight permanent precipitate is 

 formed. This precipitate is dissolved by adding 50 cc of a 4 to 6 per cent 

 solution of sodium potassium tartrate. The sample is now diluted to about 200 

 cc, solid sodium bicarbonate and starch water added, and the solution titrated 

 with standard iodin. 



TOTAL ARSENIOUS OXID, METHOD III (PROVISIONAL). 2 



SOLUTIONS REQUIRED. 



The same solutions as were required for Method II. 



METHOD. 



Boil 0.4 gram of the finely ground green with 25 cc of sodium acetate (con- 

 taining 12.5 grams of the crystallized salt) for 5 to 10 minutes. Add concentrated 



!Has been once recommended by a referee as "optional official." This method can also be 

 used to determine soluble arsenious oxid. 

 2 Has been recommended once by a referee as an "optional official" method. 



