STUDIES OP THE PINK BOLLWOEM IN MEXICO 49 
mercial machine was to obtain capacity equal to the output of an 
average gin and still to maintain the machine on an economical 
and effective basis. This matter was taken up actively by R. E. 
McDonald, of the Texas Department of Agriculture, and owing to 
his efforts rapid progress has been made in developing satisfactory 
machines. 
Machines developed in the United States may be grouped in two 
general classes according to the principles on which they operate. 
In the machines of one group the seed is heated by hot air and to some 
extent by contact with heated parts of the machine. Machines of 
the other group inject live steam into the seed mass itself. Tests 
were conducted with one machine of each group at Tlahualilo, in 
1922. 
DRY HEAT PROCESS 
In January, 1922, the Texas Department of Agriculture sent a 
machine of the dry-heat type to Tlahualilo and tested it there. This 
machine consisted of a large drum containing a group of steam pipes, 
all fixed on a central axle. It is set at a slight angle, and on opera- 
tion the entire machine, drum and pipes, revolves. Flanges on the 
inside of the drum carry the seed up and drop it between the steam 
pipes. The seed moves forward through the drum on account of the 
tilt of the machine. As a result of exhaustive tests, McDonald and 
Scholl 16 reached the following conclusion: "Our tests indicate that 
cottonseed uniformly exposed to dry heat for three and one-half 
minutes and discharged at 145° F. will be rendered free of living 
pink bollworms." They found further, from numerous experiments 
detailed in their report, that injury to germination begins at a cer- 
tain temperature which is somewhere near 165° F. 
It should be mentioned that tests with commercial machines and 
laboratory tests in an electric oven do not give data directly com- 
parable. In the practical operation of a disinfecting machine, the 
machine temperature will necessarily vary according to the tem- 
perature of the seed before treatment and the quantity of seed that 
E asses through the machine at any one time, the object of course 
eing to heat all the seed to a required temperature. Consequently 
the temperature of the seed on discharge must be used as the basis 
in the data obtained. With the laboratory tests, an oven in which 
constant temperature could be maintained was used, and the quan- 
tity of seed in any one test was so small that no accurate discharge 
temperatures were obtainable. Therefore, in these tests the oven 
temperature forms the basis of comparison. 
The Texas Department of Agriculture left its machine at Tlahualilo 
when its tests were completed. Later, to reinforce the data, the 
writer independently conducted similar tests with the same machine. 
In these tests seed taken directly from a seed house was used. It 
was fed into the hopper by hand. Irregularity in feeding is partly 
responsible for the irregular discharge temperatures obtained and the 
differences in steam pressure required to bring the seed to a certain 
temperature. A sample of from 1 to 2 bushels per test was caught 
as it came out of the machine and spread immediately on a wire 
screen, so that it cooled as quickly as possible. After cooling, all 
«R. E. McDonald, and Q. J. Scholl. Disinfecting cotton seed to prevent the spread of the pink boll- 
worm. Texas Dept. Agr. Bui. 71, pp. 38, illus. 1922. 
