28 BULLETIN 1115, U. S. DEPARTMENT OF AGEICULTUKE. 



content. Carbon dioxid is taken up until all of the calcium present 

 in the form of the oxid or hydrate is completely carbonated, at 

 which point the increase in water-soluble arsenic oxid also ceases in 

 most cases. 



The different types of commercial contaL ers tested may be ranked 

 m the following order: Sheet-metal drum, in which practically no 

 change occurred; heavy hardwood barrel; veneer drums (both un- 

 Imed and paper lined) ; sugar barrels (paper lined and unlined) . 



Of the calcium arsenates examined^ none of those stored in sheet- 

 metal drums or in tight hardwood barrels, with possibly one excep- 

 tion, suffered sufficient change in 20 months to be injuriously affected 

 for use from the standpoint of plant toxicity. 



In a few cases where calcium arsenate was stored in unhned and 

 in paper-lined veneer drums, and in unlined and in paper-lined sugar 

 barrels, the calcium arsenate at the end of the 20-month period 

 contained soluble arsenic oxid in sufficient amount to make doubt- 

 ful its safety for application on certain foliage. 



The slight changes in the chemical composition of calcium arse- 

 nate under certain conditions of packing during long storage can be- 

 practically completely avoided by the use of tight sheet-metal drums. 



ADDITIONAL COPIES 



OF THIS PUBLICATION MAY BE PROCURED FROM 



THE SUPERINTENDENT OF DOCUMENTS 



GOVERNMENT PRINTING OFFICE 



WASHINGTON, D. C. 



AT 



10 CENTS PER COPY 



