﻿STUDIES OF THE PINK BOLLWOEM IIST MEXICO 



51 



ately before and one immediately after the sample for examination 

 was taken, and determining the temperature of the seed in these 

 buckets. The difference between the two temperatures in most of the 

 tests can likewise be ascribed to differences in feeding and to varia- 

 tions in steam pressure. The temperature readings should more or 

 less represent the minimum and maximum for each sample examined. 

 Next, a series of tests was conducted in which the period of ex- 

 posure was decreased by lowering the discharge end of the machine. 

 Otherwise the method of operation was identical with that in the 

 first set of tests. The results are given in Table 43. 



Table 43. — Tests conducted with a dry-heat disinfecting machine for destruction of 

 the pink hollworm in cotton seed 



[Time of exposure ranging from 1 minute to 3J^ minutes] 



Test 

 No. 



Steam 

 pressure 



Time of 

 exposure 



Number 

 of larvse 

 in test 



Temperature 

 of seed on dis- 

 charge 



Mortality 





Pounds 



Minutes 





Degrees F. ■ 



Per cent 



256 



33-36 



lM-2}^ 



(■) 



130 -132.5 



(1) 



255 



37 



lM-2}^ 



17 



139 -138 



70.6 



257 



39-39 



134-23^ 



20 



141 -140.5 



100 



252 



26-26 



m-i'A 



19 



141. 5-144 



100 



258 



47-45 



1M-2M 



26 



146. 5-143 



96.1 



254 



40-38 



1 -m 



14 



148 -143.5 



100 



259 



49-48 



1M-2M 



36 



148 -145 



100 



263 



35-37 



1 -2K 



32 



147 -151 



100 



1 No examination. 



The result shown in these two tables tends to substantiate the con- 

 clusion, drawn by McDonald and SchoU,^^ that seed exposed to dry 

 heat so that it attains a temperature of 145° F. in a period of 33^ 

 minutes is effectively disinfected.^* That 100 per cent mortality 

 is not obtained by shorter exposures, even though a temperature of 

 145° is recorded, is no doubt due to the fact that the interior of 

 individual seeds, when immediately cooled, does not attain the 

 temperature recorded by the seed if bulked for a short time after 

 exposure. 



LIVE-STEAM PROCESS 



The type of machine just discussed, although found to be effective, 

 heats the seed rather slowly. Also, a machine of greater capacity 

 was desired to meet the needs of large gins ^^ where the installation 

 of machines of the first type with proper capacity would be an 

 expensive item. To meet these requirements a machine was de- 

 veloped in which the seed is heated by injecting live steam into the 

 seed mass. Much more rapid heating is brought about in this 

 manner. A machine of this type was sent to Tlahualilo and tested 

 by J. C. Woodward. 



The machine consisted of three inclosed 10-inch screw conveyors. 

 The seed is fed into one end of the top conveyor and is discharged 

 at the opposite end of the bottom conveyor. Immediately under- 

 neath each conveyor is a partly inclosed steam pipe. In the upper 

 side of this pipe are a number of small perforations through wmcli 



>» R. E. McDonald, and O. J. Scholl. Op. cit. 



" In experiment No. 268, a temperature of lir/' I'", was reached, but the mortality was loss than 100 per 

 cent. It will be noted, however, that the e.xpo.sure was only 2\4. ininutes. 



'» Later experiments have shown that the capacity of the machine can be Increased indefinitely by in- 

 r-reasing its size. 



