558 STATE BOARD OF AGRICULTURE. 



position by cloth pads. Thus any little overflow of mercury that might 

 occur in making transfers of gas samples was caught safely in the 

 supporting jar. Three sizes of the containers were used, viz. 250 c. 

 c, 500 c. c, and 900 c. c. capacity. The larger size served mostly in 

 preparing large stock supplies of air or of "air and insecticide vapor" 

 to be used in the respiration experiments. Mercury is so bouyant 

 that insects, (such as grasshoppers and beetles) rested entirely on the 

 surface, scarcely making a dent in it. 



The measuring-compensating burette outfit is represented in Fig. 

 4 along with one form of gas pipette used. Two gas burettes "M" and 

 '"C" were supported side by side and connected through adjacent out- 

 lets of the heavy two-way cocks at the top with the equal arms of a 

 mercury manometer. The shape of the manometer that worked best is 

 well represented in the figure. It was made of heavy clear glass. The 

 lower, wider portion had a tube diameter of 3 millimeters. The bore 

 of the narrower upper arms was 1 m. m., and they stood 1 cm. apart. 

 At the back of these arms was pasted a scale. The whole manometer 

 was IG cm. high — the lower, wide portion being 7 centimeters. The 

 two-way cocks were long, with almost parallel sides and were care- 

 fnilly ground to make them gas-tight. The free outlet tube of "M" was 

 fitted with the thimble device already described in connection with the 

 respiration container. The measuring burette "M" was 85 cm. long and 

 was graduated to 100 cubic centimeters. A bulbous portion at the 

 top, of 50 c. c. capacity, permitted the remainder of this burette to be 

 of such diameter that graduations to 0.05 of 1 c. c. could be easily 

 read with the naked eye. "C" was graduated to 80 cubic centimeters. 

 (Another outfit was obtained exactly like the one figured except that 

 its measuring burette had no bulb at the top and therefore small 

 amounts of gases could be measured. This was not often needed how- 

 ever.) 



The cocks at the lower ends of the burettes were fastened in securely 

 by means of long rubber stoppers and these could be removed in case 

 it became necessary to clean the burettes with a brush. The lower 

 cocks were connected through a U-tube with a single aspirating mercury 

 bottle, "B." The tube connections were of such length that the mercury- 

 bottle might be lifted a few inches above the tops of the burettes. 



The screw-supports represented in the figure were a very satisfactory 

 and necessary part of the outfit. The tops of these supports (25 cm. 

 square) could be steadily raised or lowered by simply turning wheel, 

 "w." As alread}^ mentioned the compensating burette would enable 

 gases to be measured in burette "M" — the volume equivalent to that at 

 0° C. and 760 m. m. pressure being given directly. Before the appa- 

 ratus could be used in that way, however, it was necessary to place a 

 certain amount of air in the compensating tube under the proper pres- 

 sure. 



A calculation was made to determine the volume of 50 c. c. of dry 

 air, at 0° C. and 760 m. m. pressure, when measured moist at the 

 temperature of the laboratory and the prevailing barometric jiressure. 

 This was done from the equation — 



V„ X 760 X (273 -f t) 

 V= . 



(B — W)X273 



