30 
Colorado Experiment Station 
containing one gram sodic sulfate to 10.5 milligrams in 72 hours for 
the solution containing three grams sodic sulfate per litre. The average 
for the eight determinations made is 6.4 milligrams arsenic acid 
per litre. 
The acid arsenate is more readily attacked even by these weak 
solutions than the ordinary arsenate of lead; but both yield significant 
quantities. 
Previous experiments had inidcated that sodic chlorid (common 
salt) is much more vigorous in its action on lead arsenate than the sodic 
sulfate or Glauber’s salt. Sodic chlorid is not present in large 
quantities in our soils and for this reason I used only one-half as much 
sodic chlorid as sodic sulfate, i. e., one-half, one, and one and a half 
grams to the litre. As the amounts dissolved and the differences are 
greater I will state them in tabular form. Ordinary lead arsenate is 
Pbi(As 04 ) 2 , the acid arsenate is PbHAsO*. The results are stated in 
milligrams of arsenic acid. 
p2 gram NaCl per litre_ 
1 gram NaCl per litre_ 
i l / 2 gram NaCl per litre. 
small quantities. 
1 gram Na^COs per litre. | 
Ordinary 
A cid 
J 24 hrs. 
31.2 
68.6 
1 72 hrs. 
72.4 
f 24 hrs. 
32.3 
74.6 
\ 72 hrs. 
48.8 
95 -i 
f 24 hrs. 
36.9 
108.4 
( 72 hrs 
47.6 
ii 34 
soda) was used in solutions one 
half as 
because it is 
; present in our soils 
in quite 
Ordinary 
Acid 
J 24 hrs. 
48.1 
H 4-5 
( 72 hrs. 
56.7 
131*1 
J 24 hrs. 
44.2 
157-6 
( 72 hrs. 
56.7 
160.9 
( 24 hrs. 
544 
1 57 - 1 
y 72 hrs. 
55-0 
158.7 
The ordinary lead arsenate, Pb^AsCE^, is attacked a little more 
freely by water containing only a comparitively small quantity of 
sodic sulfate than by pure water and the amount dissolved increased 
slightly when we increased the amount of sulfate from one and two 
to three parts per thousand. Even small amounts of soda chlorid 
and carbonate decompose the arsenate to a marked extent. The 
acid arsenate, with thirty per cent or more of. arsenic acid, is at¬ 
tacked more vigorously by each of these substances, sodic sulfate, 
sodic chlorid and sodic carbonate, than the ordinary arsenate with 
about 26 per cent of arsenic acid. This difference is quite im¬ 
portant as the acid arsenate is coming into more general use. 
