BOLL WEEVIL CONTROL BY USE OF POISON. 3 
KIND OF POISON TO USE. 
In the various studies which have been conducted by the writers, 
nearly every known type of arsenical has been tested, but the first 
generally successful results were secured from the use of an im- 
_ proved type of arsenate of lead. This was soon replaced by calcium 
arsenate, and this chemical remains the best which has been found 
for this purpose so far. Tests were conducted with both liquid and 
dry applications, and it was found that with the liquid spray a 
slight degree of control was secured, but not nearly enough to make 
the operation profitable. 
POISON SPECIFICATIONS REQUIRED. 
When calcium arsenate was first tested it was found that the ma- 
terial as then prepared was not safe for use on cotton plants, owing 
to the injury caused by burning of the foliage. This was due to the 
excessive amount of water-soluble arsenic present. It was found 
that it was possible to make calcium arsenate without this high per- 
centage of soluble arsenic, and the type which is now recommended 
for this work is absolutely safe for use on plants. Not all calcium 
arsenate, however, is of this safe type. Anyone attempting this 
work should purchase the calcium arsenate on specifications describ- 
ing its composition. The specifications advised are as follows: 
Not less than 40 per cent arsenic pentoxid.. Not more than 0.75 
per cent water-soluble arsenic pentoxid. Density not less than 80 
or more than 100 cubic inches per pound. 
Calcium arsenate was almost unknown as an insecticide when these 
experiments were inaugurated, and its production had been at- 
tempted by only a few manufacturers. Recently, however, almost all 
imsecticide manufacturers have undertaken its production. While 
its manufacture is comparatively simple, some experience is required 
to produce a thoroughly satisfactory material. Undoubtedly this 
difficulty will decrease rapidly as the manufacturers gain more ex- 
perience in the production of calcium arsenate and the quality of 
the material becomes standardized, but for the present it is still ad- 
visable to make purchases only on the specifications recommended. 
Tf the total arsenic content is too low, the material is not sufficiently 
poisonous to control the weevil. If the proportion of water-soluble 
arsenic is too high, plant injury will be the result. Some lots of 
calcium arsenate have been found which killed the cotton plants 
within a few hours after applcation. It is also important to watch 
the density of the material very closely. If it is too heavy and runs 
much less than 80 cubic inches to the pound, it is not suitable for use 
in dry powdered form and will not produce the proper type of dust 
