4 BULLETIN 1115^ U. S. DEPARTMENT OF AGEICULTUEE. 



Table 1. — Composition of calcium arsenates at the "beginning of the period of storage. 



Sam- 

 ple. 



Arsenic 

 oxid 

 (Ass 

 O,). 



Cal- 

 cium 

 oxid 



(CaO). 



Mag- 

 nesium 

 oxid 



(MgO). 



Lead 



oxid 



(PbO). 



Copper 



oxid 

 (CuO). 



Oxids 

 of iron 

 and 

 alum- 

 inum 

 (R2O3). 



Anti- 

 monic 

 oxid 



(Sb-. 

 O5). 



Acid- 

 insol- 

 uble 

 mate- 

 rial. 



Loss on 

 igni- 

 tion. 



Total. 



Carbon 

 dioxid 

 (CO2). 



Water- 

 soluble 

 arsenic 

 oxid 

 (Ass 

 0,). 





Per ct. 



Per ct. 



Per ct. 



Per ct. 



Per ct. 



Per ct. 



Perct. 



Per ct. 



Perct. 



Perct. 



Per ct. 



Perct. 



A'l" 



40.55 

 40.18 



43.16 

 39.76 



1.82 



1.88 



Trace. 

 0.91 





0.44 

 2.51 



0.02 

 .05 



0.45 

 .44 



10.88 

 10.24 



97.32 

 95.97 



2.31 



2.7s 



0.02 



AS.. 





.08 



AW. 



42.95 



42.76 



1.41 



Trace. 





.40 



.07 



.16 



8.96 



96.71 



1.78 



.08 



BT. 



41.12 



40. 57 



1.34 



Trace. 





.60 



.16 



.23 



13.90 



97.98 



3.C2 



.20 



BS.. 



40.81 



38.96 



1.78 



0.70 



0.70 



2.10 



.19 



.57 



11.40 



97.21 



5.30 



.35 



BW. 



40.58 



39.89 



2.08 



Trace. 





1.12 



.21 



.62 



11.85 



96.35 



3.44 



.69 



CT.. 



39.35 



36.92 



.22 



9.48 





.52 



.53 



.24 



8.85 



96.11 



3.30 



.83 



cs.. 



41.59 



43.06 



.38 



.77 





.38 



.50 



.44 



8.99 



96.11 



4.47 



.15 



J^'T . 



44.10 



43.80 



.48 



.63 





1.42 



.14 



.62 



4.88 



96.07 



1.40 



.00 



i'S.. 



45.07 



42.87 



.32 



.77 





1.41 



.21 



.45 



5.05 



96.15 



1.91 



.03 



HT. 



41.58 



41.04 



.82 



.72 





2.22 



.11 



1.08 



6.72 



94.29 



1.33 



.10 



HS . 



42.37 



42.05 



1.33 



.70 





1.54 



.11 



1.00 



6.33 



95.43 



1.07 



.10 



HW 



43.10 



40.35 



3.37 



.28 





2.08 



.07 



1.09 



6.86 



97.20 



.91 



.11 



IT... 



40.91 



43.16 



.75 



1.36 





1.50 



.08 



.71 



8.05 



96.52 



5.95 



.08 



IS... 



44.40 



43.16 



.53 



.73 





.86 



.19 



.77 



6.08 



96.72 



5.69 



.39 



JW . 



45.65 



40.55 



1.18 



.32 





.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 CT, 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 apprecia^ble 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 



