298 Ai/rinilfnnil Chemistry. 



in use. In one case the sample is extracted with a hot 33 per cent 

 solution of sodium acetate, while in the other case it is extracted 

 for several days with cold water and the amount of arsenic in 

 solution estimated. The former method apparently shows more 

 nearly the amount of soluble arsenic that may be present, while 

 the latter treatment more nearly simulates conditions to which 

 the insecticide is exposed in the field. 



Control laws have been passed by some suites to regulate thr 

 composition and sale of insecticides as lias been done in the case 

 of commercial fertilizers and feeding stuffs. In some cases, spe- 

 cial stipulation is made with regard to the amount of free ar- 

 senious oxide permissible in Paris green. Idaho allows a max- 

 imum amount of six per cent for this constituent and California 

 allows but four per cent. 



Green arsenoid is the trade name for a compound resembling 

 Paris green in composition and effects. It contains no acetic 

 acid but is formed from copper oxide and arsenious oxide, and 

 is technically known as copper arsenite. The pure compound 

 contains about 53 per cent of arsenious oxide. Sodium sulphate 

 or Glauber's salt is a by-product in the process of preparation 

 and may occur together with sand and other impurities in sueh 

 an insecticide; they should, however, be present in only small 

 amounts. The following data from an analysis of green arsenoid 

 illustrates the relative effect of sodium acetate solution and cold 

 water upon Hie ;irsenic of insecticides : 



Free areenious acid Per cent 



(extracted with sodium acetate) ............. ........ 3 23 



(extracted with cold water) ......................... 5.88 



This insecticide has given excellent results when mixed with 

 lime to "bind" the soluble arsenious oxide. 



London purple was imported from England by Hessey in 1^7^ 

 as a substitute for Paris green in destroying the potato beetle. 

 It is prepared by boiling a purple residue from the dye industry. 

 containing free arsrnious ni-id. with slaked lime. Calcium ar- 

 senite is formed at first, but by -ul>se<|iient hoilincr and exposure 



