﻿STUDIES OP THE PINK BOLLWOKM 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 ^^ 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 

 passes through the machine at any one time, the object of course 

 being 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. K. McDonald, and O. J. Scholl. DlBlnfcctinR cotton seed to prevent the spread of the pink boII< 

 worm. Texas Dept. Agr. Uul. 71, pp. 38, lllu.s. 1022. 



