﻿ARSENIOALS. 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 con 

 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 investigat ;ioi i . 

 The analyses of four additional samples showed the following variar 

 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 commercial quantities. In preparing sodium arsenate contain- 

 ing 45 per cent of arsenic oxid, nitrate of soda (Na 2 M0 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 about 60 per cent 

 of arsenic oxid. Sample 31 cdntains 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. 



