32 INSECTICIDE STUDIES. 



I'AIIIS 



The analyses of a large number of samples of Paris (ireen arc given 

 in Table II. together with notes that aid in explaining the methods 

 of analysis used. Whenever the method of analysis was given in the 

 <rigin-.il publication it i> quoted in full, not only in this table, but 

 throughout the bulletin, in order that the reader may judge for him- 

 self of its accuracy. In a number of cases in which only one or two 

 constituents were determined in samples of Paris greens the average 

 of all the result* is given, mentioning, however, the number that fall 

 below the generally accepted standard for such goods. 



METHODS. 



The method of determining arsenious oxid in samples Xos. 1 to U, 

 inclusive, was a< follows: 



\\Viirli 1 Lirani of the matt-rial into a beaker, add .'-JO cc of strong hydrochloric acid 

 and digest at a temperature below the boiling point, adding small quantitiesof KC10 3 

 at moment intervals. Continue lieatin.tr until the odor of chlorin lias disappeared, 

 dilute with water, add ammonia in slight exce.-s. cool, add magnesia mixture drop 

 by drop. stirring vigorously, and let stand twelve hours. Filter, wash with ammonia 

 water, and dry. Ih-tach precipitate from lilter and iirnite lilter, usin^ ammonium 

 nitrate. Transfer tlie ]>i > ecij)itate to a porcelain crucible and heat for a while on an 

 iron plate and linally in the direct flame. Add lilter ash and wei.irh as ina.iriH'siuni 

 pyr< -arsenate. 



In. simples No-. :;? to .">.">. inclusive (19 samples), the following method 

 was uM-d for determining soluble arsenious oxid: 



Allow 0..") if ram of the ^reen to stand in suspension in 50 cc of distilled water in a 

 stoppered cylinder for one week, with occasional shaking, and titrate an aliquot 

 littered portion of this solution for arsenious oxid. 



The method for determining total arsenious oxid in samples No>. r! 

 to M. inclusive, wa- practically the same as that used for samples Nos. 

 1 to ',. inclusive. 



In determining total arsenious oxid in .simple- No*. ll.s to l>b4, 

 indu-ivc (n-j samples), the method given in Bulletin <>' s . Hureau of 

 Chemistry. I'. S. I)e])artment of Agriculture, for the total arsenious 

 oxid in Pari> (ireen wa- u-ed. In determining copper the electro- 

 lytic method wa^ used. In determining soluble arsenious oxid 1 gram 

 wa- -u-])ende(l in iJMin << of water and allowed to >tand over twenty- 

 four hours in a >toppered llask. with occasional shaking. The arseniou- 

 oxid going into solution was titrated with iodin solution. 



The soluble arsenious o\id in .simple No. _'< \va- determined by 

 extracting 1 gram of Paris (Jreen with 4<><> << of water for nine 

 day-, with occasional >haking. and titrating the arsenious oxid in an 

 ali<|ii't portion of the resulting solution with iodin. 



