4 BULLETIN 875, U. S. DEPARTMENT OF AGRICULTURE. 
cloud to cover the cotton plants thoroughly. Likewise, if the mate- 
rial is too light and runs much over 100 cubic inches per pound, it is 
blown away from the plants too rapidly by any light air currents. 
SEND SAMPLES OF CALCIUM ARSENATE FOR ANALYSIS. 
The best way to make sure of having the proper grade of calcium 
arsenate is to send a sample to the Delta Laboratory at Tallulah, La., 
for free analysis. This analytical service was started by the United 
States Department of Agriculture last season and if possible will be 
continued until the quality of calcium arsenate on the market becomes 
more uniform. Every cotton planter who purchases calcium arsenate 
for this work is invited to send in samples and he will be given an 
immediate report as to whether or not the material is satisfactory 
for use in cotton dusting. For this purpose it is advisable to take at 
least two or three samples from as many different packages. Prob- 
ably the best plan is to sample 1 package in every 10 purchased. 
Half-pound samples should be taken from each and packed separ- 
ately. The complete record of each sample should be packed with 
that sample, giving its full history, including name of manufacturer, 
when purchased, size and type of package, condition of material, 
analysis claimed by manufacturer, etc. 
USE OF MIXTURES NOT RECOMMENDED. 
The only chemical now recommended for boll-weevil poisoning 
consists of calcium arsenate which conforms to the specifications de- 
scribed. Attempts have been made to utilize various mixtures of 
arsenicals or dilutions of calcium arsenate. It is quite possible that 
some of these may prove satisfactory in the future, but with our pres- 
ent information it is advisable to adhere strictly to the use of cal- 
cium arsenate without the addition of any diluent whatever. 
SUPPLY OF CALCIUM ARSENATE AND DUSTING MACHINERY AVAILABLE. 
Prior to 1919 the production of calcium arsenate was so limited 
that it was difficult to secure a sufficient amount to conduct the ex- 
periments desired in this work. During 1919, however, interest in its 
production was stimulated to the point where probably 3,000,000 
pounds were sold for cotton-dusting work. It appears that a fairly 
ample supply of calcium arsenate will be available for 1920. This is 
especially true in view of the probable shortage of dusting ma- 
chinery. It has been found that successful results can not be se- 
cured unless special types of dusting machinery are utilized. These 
machines must be prepared for this particular purpose and their de- 
velopment has been considerably slower than that of the poison. At 
the present time the supply of machinery available is hardly suf- 
ficient to serve for the proper application of the poison already sold 
by the various manufacturers. 
