﻿ARSENIC ALS. 13 



gators. A sample of barium arsenate (sample 71, Table 4) was pre- 



Eared by adding a solution of arsenic acid to a solution of barium 

 ydroxid with constant stirring. The details were as follow.-;: 

 Dissolve 546 grams of barium hydroxid (Ba(OH) 2 .8H 2 0), containing 

 240 grams of oarium, in 3 liters of water to which 300 cubic centi- 

 meters of commercial arsenic acid, containing 0.4 gram of arsenic 

 oxid per 1 cubic centimeter, has been added. After this mixture has 

 been thoroughly stirred, the precipitated barium arsenate soon settles. 

 Then wash the precipitate several times by decantation, filter it on 

 a Buchner filter, dry and pulverize it, and finally pass it through 

 a 100-mesh sieve. The theoretical composition of tribarium or- 

 thoarsenate (Ba 3 As 2 8 ) is as follows: Barium (59.7 per cent) and 

 arsenic oxid (33.32 per cent); that is, the ratio of arsenic oxid to 

 barium is 1 to 1.8. The ratio for the sample made in the laboratory 

 was 1 to 1.9, showing the presence of a slight excess of barium. Its 

 insecticidal value is discussed on page 38. 



Copper barium arsenate mixture (sample 74, Table 4) was made as 

 follows : A solution containing 360 grams of copper sulphate was mixed 

 with 275 grams of arsenic oxid. No precipitate resulted. A dilute 

 solution of barium chlorid was added and then barium hydroxid un- 

 til the solution was but slightly acid. The mixture of copper and 

 barium arsenate and barium sulphate was then thoroughly stirred 

 and allowed to settle. The precipitate was washed several times by 

 decantation and then was separated by filtering on a Buchner filter. 

 The precipitate was finally dried, ground, and passed through a 100- 

 mesh sieve. Its adhesive and fmigicidal properties have not been 

 tested, but its insecticidal powers are discussed on pages 38 to 46. 



Aluminum arsenate (sample 73, Table 4) was prepared by mixing 

 a solution of aluminum sulphate with arsenic acid. The precipitate 

 was washed, filtered, and dried. The insecticidal results of this 

 product are discussed on pages 38 to 42. 



Copper arsenate was prepared by mixing a solution of copper sul- 

 phate with arsenic acid and then adding ammonia. The percentage 

 of water-soluble arsenic oxid in this product was so high that no ad- 

 ditional tests were made with the sample. 



Zinc arsenate has been prepared by several investigators. The 

 sample prepared in this study was made by mixing a solution of zinc 

 chlorid with arsenic acid. Its physical properties did not seem to 

 warrant further study. 



COMBINATIONS OF ARSENICALS WITH FUNGICIDES AND OTHER MATERIALS. 



In order to reduce the cost of spraying, various combinations of 

 arsenicals with fungicides are frequently made. The arsenicals are 

 also mixed with other substances, like glue and casein, to increase the 

 length of time the arsenicals will adhere to the foliage or fruit. 



While some of these combinations are frequently made, very little 

 exact knowledge as to the chemical changes which take place in them 

 is available. Accordingly, an investigation was undertaken to 

 obtain information on the changes which occur in some of the im- 

 portant combinations involving arsenicals. One pound of powdered 

 acid lead arsenate per 50 gallons of water is recommended as satis- 

 factory for most commerical spraying. Acid lead arsenate at 

 this rate and other arsenicals in corresponding amounts, depending 

 on their arsenious or arsenic oxid contents, were used in the tests. 



