Vn] INSECTICIDES AND FUNGICIDES 69 



31 DETERMINATION. 



Treat 2 grams of the original sample, if in the form of a powder, or 4 grams, if 

 a paste, as directed under 12 through "Filter through a dry filter." 



Place 250-500 cc. of the clear filtrate in an Erlenmeyer flask, add 3 cc. of con- 

 centrated sulphuric acid and evaporate on a hot plate. When the volume is re- 

 duced to about 100 cc, proceed as directed under 22 to "Subtract from the cor- 

 rected titration reading." Calculate and report as per cent of water-soluble arsenic 

 oxid (AsiOs). 



CALCIUM ARSENATE. 



32 TOTAL ARSENIC— OFFICIAL. 



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

 to the arsenic oxid equivalent of 250 cc. of the standard iodin solution. 



The number of cc. of the standard iodin solution used represents directly the 

 total per cent of arsenic in the sample expressed as arsenic oxid (AS2O8) . 



ZINC ARSENITE. 



33 TOTAL ARSENIC.1-0FFICLA.L. 



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

 the arsenious oxid equivalent of 500 cc. of the standard iodin solution and titrating 

 a 200 cc. aliquot of the distillate. The number of cc. of the standard iodin solution 

 used represents directly the per cent of total arsenic in the sample expressed as ar- 

 senious oxid (AS2O3). 



34 TOTAL ARSENIOUS OXID.— TENTATIVE. 

 Proceed as directed under 7 or 8. 



COPPER CARBONATE. 



35 COPPER OXID.— OFFICIAL. 



Dissolve a weighed quantity of the substance in dilute nitric acid and deter- 

 mine copper as directed under 13 or 14. 



BORDEAUX MIXTURE. 



36 MOISTURE.-OFFICIAL. 



(a) Powder. — Dry 2 grams to constant weight at 105°-110°C. and express the 

 loss in weight as moisture. 



(b) Paste. — Heat about 100 grams in an oven at 90-100°C. until dry enough to 

 powder readily, and note the loss in weight. Powder this partially dried sample, 

 and determine the remaining moisture in 2 grams as under la). Determine car- 

 bon dioxid, as directed under 38, both in the original paste and in this partially 

 dried sample. Calculate the total moisture by the following formula: 



M = a + (100-a) (b + c) - d in which 



M = per cent total moisture in original paste; 



a = per cent loss in weight of original paste during first drying; 



b = per cent loss in weight of partially dried paste during second drying; 



c = per cent carbon dioxid remaining in partially dried paste after first 



drying; 

 d = per cent total carbon dioxid in original paste. 



