EXPERIMENT STATION BULLETINS. 451 



gasoline-treated chamber. Nevertheless, when run for longer periods 

 afterward, the "extract plus hydroquinone" mixture in the gasoline 

 chamber showed a reddish brown color not nearly so deep as that in 

 the check gas-chamber containing air only, and the volumetric results 

 then agreed with the results of the other experiments. The reason for 

 the apparently contradictory results of the first and second parts of 

 these two experiments was not understood until later. About a year and a 

 half after these first experiments had been made (i. e. after the effect of 

 gasoline upon the tissue reductase had been studied) it was decided to 

 run a few more tests with gasoline-vapor, using a different method, in 

 order to find out more surely if possible, the influence of this insecticide 

 upon the absorption activity for oxygen of "insect tissue-extract plus 

 hydroquinone" solution. The method decided upon was the old one 

 (described in Part 1, Tech. Bull. II) in which the percentages of the 

 gases present were determined at the beginning and at the end of the 

 test period; but a different arrangement of gas-containers and gas- bur- 

 ettes was made to adapt the method to this problem. 



The arrangement of containers and burettes in the apparatus used is 

 represented in Fig. III. As may be seen, the apparatus is an 

 adaptation of that shown in Fig. 1, with the circulating pumps and 

 absorption flasks left out. Thei'e were two duplicate systems — gasoline- 

 vapor-air was used in the gas-chamber of one system and pure air in the 

 other. Hydroquinone burettes enabled one to introduce the hydroquinone 

 as described in the case of apparatus Fig. I. The two gas-containers had 

 each two two-Avay cocks, and these enabled one to adjust the mercury 

 manometers and to take gas samples for estimation from each container 

 at the beginning and at the end of test-periods. The gas-burettes per- 

 mitted one to keep close check upon changes in gas-volume in each sys- 

 tem, the readings being made at the known temperature and barometric 

 pressure. From the percentage determinations (since the cubic contents 

 of each system was known) one could figure the amount of oxygen used 

 and of carbon dioxide given off at 7G0 m. m. pressure and 0°C., as well 

 as the exact percentage of gasoline to which the "insect-extract plus hy- 

 droquinone'' solution had been subjected in the test. A set of results ob- 

 tained with this arrangement of apparatus is given in table III. The 

 total oxygen absorbed in the pure air chamber exceeded the total oxygen 

 absorbed in the gasoline-air chamber, and the ratio ^ was a little 

 higher in the gasoline-air chamber. By this method, as with the former 

 method, however, it was found that if fresh extract were used for a short 

 period, the result might be contradictory to that given for a much longer 

 or for a later period with the same extract. 



