14 INSECTICIDES AND FUNGICIDES. 



arid with hydrochloric acid, taking care that all lumps of sodium car- 

 bonate on the bottom are acted on by the hydrochloric acid. Sodium 

 bicarbonate is now added in excess and the solution of iodin run in, 

 drop b}^ drop, using starch to read the end reaction. (Sometimes the 

 solution gets dark toward the end of the titration. This must not be 

 confused with the final dark-blue color given by the iodin and starch.) 



From the number of cc of iodin solution used and the weight of 

 arsenious oxid taken, the value of each cc of iodin in arsenious oxid 

 can be determined. 



Two grams of Paris Green are weighed out and transferred to a 250 

 cc flask and about 100 cc of water and 2 grams of sodium h\ r drate 

 added. This solution is boiled for 5 to 10 minutes, or until all of the 

 green particles have changed to red cuprous oxid. It is then cooled to 

 room temperature and the volume made to 250 cc. The well-shaken 

 liquid is filtered through a dry filter and 50 cc taken for analysis. 

 The analysis is carried out from this point forward the same as when 

 we standardize the iodin solution. 



Copper oxid. The cuprous oxid obtained in the above method by 

 boiling the Paris Green with sodium hydroxid is poured on the filter 

 (after taking an aliquot portion of the solution for the determination 

 of arsenious oxid) and well washed with hot water. It is then dis- 

 solved with hot dilute nitric acid and made to a volume of 250 cc, 

 one-fifth being taken for analysis. The copper in solution is deter- 

 mined either by means of the galvanic current or, when that is not 

 handy, in the following manner: The nitric-acid solution is made alka- 

 line with sodium carbonate, then made slightly acid with acetic acid, 

 and about ten times the weight of the copper in potassium iodid added. 

 When it is all dissolved, the free iodin is titrated with a standard solu- 

 tion of sodium thiosulphate, using starch as indicator." 



Soluble arsenious oxid. In making the determination of this con- 

 stituent two methods of analysis were used, namely, the water extrac- 

 tion method and the sodium acetate extraction method. 6 



The first of these methods is carried out as follows: Treat 1 gram of 

 Paris Green with 1 liter of water (previously boiled to get rid of CO 2 

 and again cooled to room temperature) in a large flask. The flask is 

 stoppered and shaken five times each day for 10 da} 7 s. At the end 

 of this time the solution is filtered off through a dry filter. Two 

 hundred cc of this is treated with sodium bicarbonate and titrated 

 with standard iodin. This gives the amount of arsenious oxid dis- 

 solved. Because of the fact that water breaks up Paris Green on 

 standing in contact with it, some copper oxid always goes into solution 

 at the same time as the arsenious oxid does. This was also determined 



For the details of this method, see Sutton's Volumetric Analysis, 3d ed., p. 133. 

 6 See report of the associate referee in the Proceedings of the Association of Official 

 Agricultural Chemists for 1901. 



