34 F - G. HALL. 



from the compressed air-tank through a trap to prevent back 

 flow of acid was rendered dry by its passage through the exsic- 

 cating jars. 



Two filters were arranged. The first (Fig. i, Z), a 100 cc. 

 bottle containing about an equal weight of powdered and granu- 

 lated zinc. The purpose of this filter was to prevent the passage 

 of sulfuric acid. The second filter (Fig. i, G), consisting of a 

 500 cc. bottle filled with glass wool, prevented the passage of any 

 physical impurities. Tests of the air were made by allowing the 

 air as it passed out of the exsiccating chamber to bubble through 

 a methyl-orange solution for an hour. There were no indications 

 of sulfuric acid in the air. 



The manometer or flow-meter (Fig. i, M) used for the deter- 

 mination of the rate of flow of air into the exsiccating chamber 

 was constructed of glass tubing. A horizontal tube connecting 

 the two ends of a U-tube and having a small aperture between the 

 points of connection allowed the passage of air from the second 

 filter to the exsiccating chamber. The U-tube was partly filled 

 with olive oil, which was used because of its low evaporating co- 

 efficient. The passage of air through the horizontal tube in- 

 creased the pressure on the column on one side thereby lowering 

 the level. The difference of level of the liquid in the U-tube was 

 a measure of the static pressure and was an indicator of the rate 

 of flow of the air passing into the exsiccating chamber. The 

 manometer was accurately calibrated from a gas meter used 

 for such purposes by the department of physiology, University of 

 Wisconsin. A scale was placed behind the U-tube and the rate 

 of flow in cubic centimeters could be read at any time. 



A large Whithall-Tatum museum jar (Fig. i, C) was used for 

 the exsiccating chamber. Four holes were drilled through the 

 lid, one for the dry air inlet, one for the air outlet, two for the 

 inlet and outlet tubes to the dew-point apparatus. The lid was 

 fastened by a metal clamp and sealed by a rubber gasket. An 

 outlet tube connected the exsiccating chamber with a small beaker 

 containing sulfuric acid (Fig. i, O). The end of the outlet tube 

 was just far enough below the surface of the acid to indicate by 

 bubbling if the chamber was tightly sealed, and also to prevent 

 back flow of air containing water. 



