72 METHODS OF ANALYSIS [Chap. 



47 Method II.— Tentative. 

 Proceed as directed under 8. 



48 WATER-SOLUBLE ARSENIOUS OXID.— TENTATIVE. 

 Proceed as directed under 20, using 2 grams of the sample. 



BORDEAUX MIXTURE WITH LEAD ARSENATE. 



49 MOISTURE.-OFFICLAL. 



Proceed as directed under 36. 



50 CARBON DIOXID.— OFFICIAL. 



Proceed as directed under 38. 



51 COPPER.-TENTATIVE. 



Proceed as directed under 44. 



52 LEAD OXID.3— TENTATIVE. 



Dissolve the lead peroxid (which will contain a little arsenic) from the anodes 

 used in the copper electrolysis, under 51 , by means of dilute nitric acid and a little 

 hydrogen peroxid, and add to this solution the washings from both electrolyses 

 of copper. Add ammonium chlorid to dissolve any lead sulphate which may have 

 precipitated out and make the solution up to 1 liter. Concentrate a 500 cc. aliquot 

 of this solution to about 300 cc. (all hydrogen peroxid must be expelled from the 

 solution), transfer to a 400 cc. beaker and precipitate the lead as lead chromate 

 as directed under 24. 



53 TOTAL ARSENIC.i-OFFICIAL. 



Proceed as directed under 5, using an amount of the dry, powdered sample equal 

 to the arsenic oxid equivalent of 500 cc. of the standard iodin solution. The num- 

 ber of cc. of the standard iodin solution used, divided by 2, represents directly the 

 per cent of total arsenic in the sample expressed as arsenic oxid (AszOs). 



54 WATER-SOLUBLE ARSENIC OXID.-TENTATIVE. 

 Proceed as directed under 31 . 



SODIUM AND POTASSIUM CYANIDS. 



55 CYANOGEN.is— OFFICLAL. 



Weigh about 10 grams of the sample in a weighing bottle, dissolve in water, and 

 make up to volume in a liter graduated flask. To a 50 cc. aliquot add N/20 silver 

 nitrate, drop by drop, stirring constantly, until 1 drop produces a permanent tur- 

 bidity. In calculating the results, 1 equivalent of silver is equal to 2 equivalents 

 of cyanogen, according to the following equation: 



2NaCN + AgNOa = NaCNAgCN + NaNOj 



Reserve the titrated solution for the determination of chlorin under 56. 



