Vn] INSECTICIDES AND FUNGICIDES 71 



BORDEAUX MIXTURE WITH PARIS GREEN. 



41 MOISTURE.-OFFICIAL. 



Proceed as directed under 36. 



42 CARBON DIOXID.-OFnCIAL. 

 Proceed as directed under 38. 



COPPER. 



43 Method I— Tentative. 



Dissolve 2 grams of the dry powdered sample in a few cc. of strong nitric acid, 

 add 25 cc. of a 3% solution of hydrogen peroxid and warm for 5-10 minutes. Make 

 slightly alkaline with ammonium hydroxid and then slightly acid again with dilute 

 nitric acid. Transfer to a weighed 150 cc. platinum dish, add 15-20 cc. of hydrogen 

 peroxid, dilute to 100 cc. and electrolyze, using a rotating spiral anode and a cur- 

 rent not exceeding 2 amperes. After the electrolysis has proceeded for about 20 

 minutes, add to the electrolyte 0.5 gram of ferric sulphate dissolved in a few cc. 

 of water together with a drop or two of nitric acid. After all the copper is deposited, 

 wash the deposit with water by siphoning, then rinse with alcohol, dry for a few 

 minutes in an oven, weigh and calculate the per cent of copper. (Do not pass the 

 current for more than 5-10 minutes after all the copper has been deposited without 

 adding more ferric sulphate solution.) 



44 Method II. — Tentative. 



Treat 1 gram of the dry powdered sample with 20 cc. of water and 5-6 cc. of con- 

 centrated nitric acid, heat to boiling, cool, and add a slight excess of concentrated 

 ammonium hydroxid. Wash the solution and precipitate into a weighed platinum 

 dish of about 150 cc. capacity, and electrolyze, using a rotating anode and a cur- 

 rent of about 4 amperes and 3-4 volts for about 90 minutes (.or until all the copper 

 is deposited) . Wash the deposit by siphoning until the deposit is clean, being care- 

 ful not to use too much wash water. Dissolve the copper in 5 cc. of concentrated 

 nitric acid, dilute to 100 cc. and electrolyze as before, except that all the copper 

 will be deposited in 30 minutes. Wash the deposit with water by siphoning, then 

 rinse with alcohol, dry for a minute or so in an oven, weigh and calculate the per 

 cent of copper. 



45 TOTAL ARSENIC-OFFICIAL. 



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

 to the arsenious 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 arsenious oxid (AsjOs). 



TOTAL ARSENIOUS OXID. 



46 Method I.— Tentative. 



Proceed as directed under 7, using an amount of the dry, powdered sample equal 

 to the arsenious oxid equivalent of 200 cc. of the standard iodin solution. Before 

 titrating, all the copper must be in solution. The corrected number of cc. of the 

 standard iodin solution used, divided by 2, represents directly the per cent of total 

 arsenious oxid (AS2O3) in the sample. 



