ARSENICALS. 
11 
solubility in water and yielded only 3.01 per cent of arsenic oxid 
soluble in water saturated with carbon dioxid. 
London purple, originally a by-product in the manufacture of 
aniline dyes, is now made directly to a limited extent. It consists 
of arsenite of lime and arsenate of lime, with the addition of a dye. 
Table 4 gives the composition of the material used in the investigation. 
The analyses of four additional samples showed the following varia- 
tions: Arsenious oxid, 18.30 to 29.38 per cent; arsenic oxid, 0.07 to 
11.49 per cent; water-soluble arsenious oxid, 0.48 to 5.30 percent; and 
water-soluble arsenic oxid, 0.07 to 2.46 per cent. One sample showed 
24.91 per cent of calcium oxid, 2.70 per cent of magnesium oxid, and 
11.25 per cent of ferric oxid and silicon dioxid. London purple, 
therefore, is of uncertain composition and contains varying amounts 
of water-soluble arsenious oxid and arsenic oxid. On account of its 
variable character and its tendency to burn foliage, the addition of 
lime is recommended when it is used as a spray. 
Calcium and lead arsenates combined (samples 36 and 8) were 
analyzed and tested on insects. The demand for a mixed calcium 
and lead arsenate is limited. It is held by some that lead arsenate 
adheres to foliage better than calcium arsenate, so that the presence 
of a little lead arsenate in the mixture increases the adhesive prop- 
erties. The use of calcium carbonate in the mixture reduces the 
percentage of arsenic present and permits the product to be sold 
more cheaply. 
Sodium arsenate was formerly on the market in two grades, a 45 
per cent and a 65 per cent arsenic oxid product. During the past 
three or four years it has been difficult to obtain sodium arsenate 
in co mm ercial quantities. In preparing sodium arsenate contain- 
ing 45 per cent of arsenic oxid, nitrate of soda (NaN0 3 ), arsenious 
oxid (As 2 3 ), sodium carbonate (Na 2 C0 3 ), and salt (NaCl) are 
roasted together. In preparing the 65 per cent grade the salt is 
omitted. The two commercial samples (Nos. 31 and 41) correspond 
to these two grades, although sample 41 contains only 60 per cent 
of arsenic oxid. Sample 31 contains 28.44 per cent of sodium 
chlorid, sample 41, 6.14 per cent, and sample 25, 0.096 per cent. 
Calculating the results for these two samples and for sample 25 
(prepared in the laboratory) to a moisture-free basis, sample 25 
contains 60 per cent, sample 31 about 47 per cent, and sample 41 
about 64 per cent of arsenic oxid. All the arsenic present in sodium 
arsenate is water soluble. Sodium arsenate is sometimes added to 
Bordeaux mixture to produce a combined fungicide and insecticide. 
The excess lime of Bordeaux combines with the arsenic oxid of the 
sodium arsenate, forming insoluble calcium arsenate. The amount 
of sodium arsenate added and the amount of the excess lime of the 
Bordeaux are the factors which determine whether all of the soluble 
sodium arsenate is converted into the insoluble calcium arsenate. 
Potassium arsenate. — Sample 26 is a laboratory product contain- 
ing 59.39 per cent of arsenic oxid, all of which is soluble in water. 
No commercial samples of potassium arsenate are now available. 
MISCELLANEOUS EXPERIMENTAL ARSENICALS. 
The analytical results on three samples of lead arsenates and four 
samples of calcium arsenates made in the laboratory are given in 
Table 5. 
