26 METHODS OF ANALYSIS. 



From the number of cubic centimeters of iodin solution and the weight of 

 arsenious oxid used determine the value of each cubic centimeter of iodin in 

 terms of arsenious oxid. 



(2) DETERMINATION. 



Transfer 2 grams of Paris green to a 250 cc flask by means of about 100 cc 

 of a 2 per cent sodium-hydroxid solution. Boil this mixture for 5 to 10 min- 

 utes, or until all the green particles have changed to red cuprous oxid, then 

 cool it to room temperature and make the volume up to 250 cc. Filter the 

 well-shaken liquid through a dry filter and use 50 cc portions for analysis. 

 Conduct the analysis from this point as when standardizing the iodin solution. 



(c) TOTAL ARSENIOUS OXID, METHOD II (AVERT). OPTIONAL OFFICIAL. 



(1) SOLUTIONS REQUIRED. 



(a) Standard iodin solution. Prepare an iodin solution as in Method I 

 (p. 25). To standardize this solution place 1 gram of dry chemically pure arse- 

 nious oxid in a 250 cc flask, and dissolve by boiling about 20 minutes with 

 5 grams of sodium bicarbonate and approximately 100 cc of water ; cool ; add 

 hydrochloric acid until acid, and then sodium bicarbonate until alkaline ; make 

 up to the mark and titrate aliquots of 50 cc with iodin solution as in Method I. 



(6) Sodium acetate solution. Dissolve 12.5 grams of the crystallized salt in 

 each 25 cc of water. 



(c) Sodium potassium tartrate solution. Dissolve from 2 to 3 grams of 

 sodium potassium tartrate in each 50 cc of water. 



(d) Starch solution. Prepare a starch solution as in Method I. 



(2) DETERMINATION. 



Place 1 gram of Paris green in a 100 cc flask and boil for 5 minutes with 

 25 cc of the sodium acetate solution. Make to the mark, shake, and pass 

 through a dry asbestos gooch filter. Use an aliquot of this filtrate for the 

 determination of the soluble arsenious oxid by means of the iodin solution. 

 Transfer the residue on the filter to a beaker, beat up with a little water, 

 dissolve in concentrated hydrochloric acid added a drop at a time, then add 3 

 or 4 drops In excess. Transfer the whole to the 100 cc flask originally em- 

 ployed and analyze aliquots of from 20 to 40 cc. Add concentrated sodium 

 carbonate solution, a drop at a time, to each of these aliquots until a slight per- 

 manent precipitate is formed. Dissolve this precipitate by adding 50 cc of 

 the sodium potassium tartrate. Dilute to about 200 cc, add solid sodium 

 bicarbonate and starch water, and titrate with standard iodin. 



(d) TOTAL ARSENIOUS OXID, METHOD III (AVERY-HAYWOOD). OPTIONAL 



OFFICIAL. 



(1) SOLUTIONS REQUIRED. 

 Prepare the same solutions as were required for Method II. 



(2) DETERMINATION. 



Boil 0.4 gram of the finely ground Paris green with 25 cc of the sodium 

 acetate solution for from 5 to 10 minutes. Add concentrated hydrochloric acid, a 

 drop at a time, until solution is effected (about 10 cc of the acid is usually nec- 

 essary). Add concentrated sodium carbonate solution, a drop at a time, until 



