28 BULLETIN 1115, U. S. DEPARTMENT OF AGRICULTURE. 
ial “ici i 
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 contai. ers tested may be ranked 
in the following order: Sheet-metal drum, in which practically no 
change occurred; heavy hardwood barrel; veneer drums (both un- 
lined 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 unlined and 
in paper-lined veneer drums, and m 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 shght 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. ~ 
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