L ^ \ 



OTHEK THAN PARIS GREEN AND LONDON PUKI'LE. 23 



J 



Just at this point it might bo well to mention oireiunction that lime 



perhaps performs when used with Paris Green to prevent scorching 

 of the foliage. It is known, of course, that lime is added to change 

 the free arson ious oxid in the green to the less harmful salt calcium 

 arsenite, but it also seems probable that lime has a second function. 

 As the Paris Green is gradually broken up by the action of dew and 

 rain, both charged with carbon dioxid, lime would form with the 

 arson ions oxid, set free the more insoluble and less harmful compound 

 calcium arsenite, and thus prevent scorching of the foliage. Even when 

 the lime had finally all changed to calcium carbonate by the action of 

 carbon dioxid in the air, when water containing carbon dioxid came 

 in contact with it, it would render enough of the carbonate soluble as 

 the bicarbonate to act upon the arsenious oxid set free from the Paris 

 Green and form calcium arsenite. 



INSECTICIDES AND FUNGICIDES, OTHER THAN PARIS GREEN AND 

 LONDON PURPLE, THAT CONTAIN ARSENIC OR COPPER, OR BOTH, 

 AS THEIR ACTIVE CONSTITUENT. 



The methods of analysis for this group of compounds are so many 

 and diverse that but a few general principles applying to most of the 

 mixtures coming under this heading can be given. 



METHODS OF ANALYSIS AND DISCUSSION. 



The methods of analysis of Green Arsenoid and Scheele Green are 

 the same as those described for Paris Green. For White Arsenoid, 

 the same methods arc used as described in connection with London 

 Purple, except that the barium is determined by precipitating from 

 hydrochloric-acid solution with sulphuric acid. For Rough on Rats 

 some of the London-Purple methods are also used. For those compounds 

 which contain arsenic, copper, calcium, magnesium, iron, and sulphur 

 trioxid the following methods are used: 



Copper o.i'td. Dissolve the compound in hydrochloric acid and filter; 

 heat the solution to 70 C. and pass hydrogen sulphid through until all 

 copper sulphid and arsenious sulphid are precipitated; wash quickly 

 with hot water, dry, and finally burn in a weighed porcelain crucible; 

 add some powdered sulphur, cover crucible, and burn again; finally, 

 weigh the copper as the mixed subsulphid and oxid. The percentage 

 of copper being the same in both, the whole may be considered as 

 copper oxid. 



Arsenious oxid. Proceed just as in the determination of copper down 

 to the point where the arsenious and copper sulphids have been washed 

 with hot water (taking the extra precaution, however, of not using too 

 high a (loo-ree of heat in getting the original substance in solution, for 

 fear of driving off arsenious chlorid); spread the filter out and transfer 



