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STATE BOARD OF AGRICULTURE. 



which are on the market. Two of these forms are represented in Figs, 

 4 and 5 at "P." The use of various Hempel pipettes is described in 

 most recent books on gas analysis, and their manipulation in connection 

 with this work may be briefly referred to later in the paper. 



In using this apparatus to determine the normal respiration of in- 

 sect species the percentages of nitrogen, oxygen and carbon dioxide 

 were first determined for the air to be used. An air-sample of any- 

 where between 100 c. c. and 75 c. c. was measured by the measuring- 

 compensating burette. Water was placed in the thimble "th" (see Fig. 

 4.) vmtil'the rubber connecting tube was full. The solution^ in a 



Fig. 5. Apparatus used in obtaining small amounts of hydrogen or of nitrogen entirely free frcm 

 oxygen. "C" = gas container, same form as used for a respiration container. 



potash pipette was then forced over slowly through the capillary trans- 

 fer tube "t" until a drop was just ready to fall into "th." The free 

 end of "t" was then forced down firmly into the rubber connecting 

 tube. In this manner connections could be made so that all undesired 

 air was excluded and onlv the measured air was transferred. When 

 the carbon dioxide had been absorbed, the mercury ^'M" was lowered 

 slowly until, finally, tlie potash solution was drawn over in "t" just 

 into the top of the connection-tube within "th," when '*m" was closed. 

 Tests showed that all of a gas-sample, to within 0.05 c. c. could be re- 

 turned thus without drawing any of the potash solution- into "M.'- 

 The gas was then measured as before; the difference between this read- 

 ing and the first being the volume of carbon dioxide present. 



1. A solution of c. p. KOH of the strength recommended by Hempel was used. 



2. As a precaution, however, the measuring burette (M) was washed out before the next new esti- 

 mation of C02 was begun. 



