2 BULLETIN 278, U. S. DEPARTMENT OE AGRICULTURE. 
first few experiments showed that many of these were of little value 
as stomach poisons, their use was discontinued. 
A few homemade preparations were tested in the course of these 
experiments. Those used in 1912 were arsenate of iron, arsenate of 
zinc, and arsenite of lime. The methods of preparation of these ma- 
terials were as follows : 
Arsenate of iron was prepared by dissolving 4 pounds of sodium- 
arsenate crystals and 4 pounds of iron sulphate each in 2 gallons of 
hot water. The iron-sulphate solution was then poured slowly into the 
sodium- arsenate solution, the solution being stirred vigorously at the 
same time. Arsenate of iron was used at a rate equal to 0.8 pound of 
sodium arsenate to 50 gallons of water for the ordinary strength. 
The arsenate of zinc (homemade) was prepared in the same way 
as arsenate of iron, sodium arsenate and zinc sulphate being used, 
and the strength being based upon the sodium- arsenate content, the 
same as for arsenate of iron. 
Arsenite of lime was prepared by boiling 2 pounds of white arsenic 
and 2 pounds of sal soda in 1-J- gallons of water until thoroughly dis- 
solved, and this was used to slake 4 pounds of stone lime. After 
slaking, enough water was added to bring the total to 2 gallons. This 
was used at the rate of 2 pints to 50 gallons of water, which. is 
equivalent to one-fourth pound of white arsenic to 50 gallons of water. 
LABORATORY TESTS. 
During the season of 1912 the fall webworm (HypJiantria cunea 
Drury) was used for all the experiments, since this insect could be 
readily obtained in large numbers, and proved to be an ideal species 
for handling in the laboratory. Very young larvae, usually 3 or 4 
days old, were used in all the tests. The larvae were fed with foliage 
of the wild black cherry (Prunus serotina), which was found to be a 
favorite food plant of the fall webworm in Michigan. Twigs having 
from 20 to 30 leaves each were sprayed by means of a large atomizer 
of the type in which quart jars are used as a container for the liquid, 
and the stems of the twigs were placed in small glass jars containing 
water. 
After the spray had thoroughly dried, allowing from 6 to 12 hours, 
20 insects were placed on the leaves of each twig. A large paper bag 
was then placed over the twig and held to the glass by means of a 
rubber band to prevent the escape of the larvae. At each examina- 
tion the bag was removed and the dead larvae taken out and counted. 
When all the insects were dead or had pupated, as the case might be, 
the amount of foliage consumed was measured in square inches. A 
sheet of celluloid, cross-sectioned to 0.01 of a square inch, was util- 
ized for this purpose. These measurements were easily taken where 
effective poisons were used, as the young larvae died before very 
