PARIS GREEN 631 



Determination. Place half a gram of paris green in a 250 

 cubic centimeter erlenmeyer flask, add 100 cubic centimeters of 

 distilled water and agitate by shaking every few minutes through- 

 out a working period (eight hours) of a clay, keeping the liquid 

 at only 25 to 30. The next day after pouring off the clear 

 liquid, add a fresh 100 cubic centimeter portion of water and 

 repeat the treatment mentioned above. Repeat the same treat- 

 ment on a third day, in all 24 hours. Finally, combine the three 

 TOO cubic centimeter leachings, filter through a double filter and 

 determine arsenious oxid by means of standard iodin in the 

 filtrate. 



Total Copper Oxid. Met-hod I. 5 Pour the cuprous oxid (ob- 

 tained in Method I, for total arsenious oxid by boiling the paris 

 green with sodium hydroxid) on the filter and wash well with 

 hot water, after an aliquot of the filtrate has been used for the 

 determination of arsenious oxid. Then dissolve in hot dilute 

 nitric acid and make up to a volume of 250 cubic centimeters. 

 Use 50 to ioo cubic centimeters of this solution for the electro- 

 lytic determination of copper, as described on page 52, para- 

 graph (2), under "VII General Methods for the Analysis of 

 Foods and Feeding Stuffs." Bulletin 107, Bureau of Chemistry. 



Total Copper Oxid. Method 7/. Solutions Required. Stand- 

 ard thiosulfatc solution. Dissolve 24.8 grams of the crystallized 

 salt and make up to two liters. Standardize this solution against 

 chemically pure copper foil dissolved in nitric acid by the method 

 of analysis given in the following paragraph. 



Determination. Use an aliquot portion of the nitric-acid so- 

 lution of copper oxid, employed in Method I for total copper 

 oxid. Make it alkaline with sodium carbonate, then make slight- 

 ly acid with acetic acid, dilute with water, and add about three 

 or four grams of solid potassium iodid. When the potassium 

 iodid is all dissolved by shaking, titrate the free iodin with thio- 

 sulfate, using starch as indicator toward the end of the reaction. 



Total Copper Oxid. Method III.' Solutions Required. A 



5 Bureau of Chemistry, Bulletin 73, 1903 : 158; Bulletin 81, 1904 : 195 ; 

 Bulletin 90, 1905 : 95. 



6 Journal of the American Chemical Society, 1900, 22 : 568. 

 ' Bureau of Chemistry, Circular 10, 1905, Revised. 



