4 BULLETIN 1115, U. S. DEPARTMENT OF AGRICULTURE. ~- 
TABLE 1.—Composition of calcium arsenates at the beginning of the period of storage. 
Oxids F Water- 
F | ‘ Anti- | Acid- 
TR tea cr acne: Lead Copper aa monic | insol- | Losson Carbon|Soluble 
ple.| (As> | oxid | oxid oxid | oxid | sium. | OxXid | uble | igni- |Total.| dioxid aA 
Os). | (CaO). |(Mgo). | (PPO). | (Ca0)-| inum any rc BL CO2). 1 (As 
(R203). i O;). 
Per ct. | Per ct. | Per ct. | Per ct. | Per ct. | Per ct. | Per ct. | Per ct. | Per ct. | Per ct.| Per ct. | Per ct. 
40.55 | 43.16 A621 Trace.|¢.2"-<"- | 0.44 0. 02 0.45 | 10.88 | 97.32 Zor 0. 02 
AS..| 40.18 | 39.76 1.88 (0% (35 El eee ee | 2.51 05 -44 | 10.24 | 95.97 2.78 08 
AW.| 42.95 | 42.76 Te4 TACO. Ieee ook . 40 SO . 16 8.96 | 96.71 1.78 . 08 
Bea all2s) 4057 bee | Praeces | oo ee s. . 66 . 16 -23 | 13.90 | 97.98 3. 62 . 20 
BS..| 40.81 | 38.96 1.78 0. 70 0.70 2.10 19 ot LN 40r | O72 28 5. 30 35 
BW.| 40.58 | 39.89 QOS eCRAC OR te wooee 1.12 21 -62 | 11.85 | 96.35 3. 44 69 
GP) 739/35 1**36292 sy + ac: be il Pape oa 52 53 24 8.85 | 96.11 3. 30 83 
CS -.| 41.59 | 43.06 .38 La fa SMe 2 8 38 50 44 8.99 | 96.11 4.47 a5 
FT .| 44.10] 43.80 . 48 08 Ta RS eee 1.42 .14 . 62 4.88 | 96.07 1.40 - 00 
FS..| 45.07 | 42.87 ~32 a aleeet ys 4 41.41 el ~45 5.05 |-96.15 1,91 - 03 
HT.| 41.58] 41.04 - 82 ik 0) (Sic RE 2.22 a Wt 1.08 6.72 | 94.29 ig3s .10 
HS .| 42.37] 42.05 1.33 PA: | es ae Ved 4 emt 1.00 6.33 | 95. 43 1.07 -10 
HW} 43.10] 40.35 3.37 5740) ea 2.08 . 07 1.09 6. 86 | 97. 20 -91 at! 
IT...| 40.91 | 43.16 alo ya Eee Oe |, 1350 . 08 Stl 8.05 | 96. 52 5. 95 - 08 
IS...| 44.40] 43.16 soo LBS feats Sis . 86 .19 onie 6.08 | 96.7 5. 69 .39 
JW .| 45.65 | 40.55 1.18 | BOs pe ney - 92 .29 .32 5.37 | 94.60 | 2.69 .30 
| ] } | } 
It will be noted that the arsenic oxid content exceeds 40 per cent 
in every case, except that of the sample containing lead, and that 
the calcium oxid and arsenic oxid values are approximately equal. 
This is as it should be in a properly made calcium arsenate to be used 
for insecticidal purposes. The impurities are low in all cases except 
one, sample ('T, which contains more than 9 per cent of lead expressed 
as the oxid. This is probably present in the form of lead arsenate 
as a result of carelessness in manufacture. The presence of small 
quantities of lead in the other samples is doubtless caused by the use 
in their manufacture of apparatus that had previously been employed 
in making lead arsenate. The copper in sample BS apparently owed 
its origin to the presence of Bordeaux mixture, as small pieces of a 
blue material resembling this product were visible. The water- 
soluble arsenic oxid figures are reasonably low in all cases except 
two, one of which is the sample containing an appreciable quantity 
of lead. 
CARBON DIOXID AND WATER-SOLUBLE ARSENIC OXID IN STORED SAMPLES. 
The chemical criterion employed in the estimation of deterioration 
in calcium arsenate is the change in the so-called water-soluble arsenic 
oxid. All of the work quoted from the literature showed that con- 
tact with carbon dioxid in the presence of water may greatly increase 
the content of soluble arsenic oxid. The authors’ experience accords 
with this. When carbon dioxid is bubbled through an aqueous sus- 
pension of commercial calcium arsenate for a sufficient length of time, 
the quantity of arsenic oxid rendered soluble is approximately the 
same as that obtained when dicalcium arsenate is treated with 
water alone, in the same concentration. Further, calcium carbonate, 
under ordinary conditions, neutralizes arsenic acid only to the dical- 
cium arsenate stage, showing that a basic mixture tends to revert, by 
