Apparatus and Methods 79 



gas in the measuring pipette likewise produces a corresponding decreased 

 tension. As the pipette is graduated in percentages, it obviously makes 

 no difference whether the gas measured is at atmospheric or less than at- 

 mospheric pressure, provided the residual gas is at the same pressure. 

 For this reason, then, when the level of the mercury in the measuring 

 pipette B is adjusted after the oxygen is absorbed, no change is made 

 in the level of the mercury in the compensating pipette A. The reading 

 for the oxygen, therefore, represents the percentage of oxygen in carbon- 

 dioxide-free air. 



Reagent containers. To insure rapid and efficient absorption, the 

 reagent should be contained in a vessel capable of exposing a relatively 

 large area of reagent to the gas. Since the relation between the area and 

 the volume of gas depends in large part upon the amount of gas to be 

 absorbed, in the case of carbon dioxide, of which no more than 1 per cent 

 is ever present, the area may be very much less than with oxygen of 

 which over one-fifth is absorbed. The forms of reagent containers found 

 most advantageous for this type of apparatus are shown as C and D in 

 fig. 1. As will be seen, the general structure of both vessels is the same, 

 the notable difference being that D contains a large number of short glass 

 tubes which increase greatly the absorbing surface. To prevent the 

 tubes from falling out, the opening at the bottom is somewhat more con- 

 stricted than in C. Each container is so constructed that when filled 

 with the reagent the level inside and out is the same; special marks not 

 only on the inner capillary tube but also around the outer glass envelope 

 of the chamber aid in introducing the proper amount of reagent and in 

 setting the level of the reagent in the capillary. A short length of glass 

 tubing fused to the chamber projects above the level of the water in the 

 tank and, being open to the air, insures atmospheric pressure on the outer 

 surface of the reagent. This tube serves to introduce the various reagents 

 for absorbing the gases to be determined. The lower ends of both cham- 

 bers project through holes in the glass bottom of the tank, the same pre- 

 cautions for water-tight closure observed in the case of the pipettes A and 

 B being also here taken. 



REAGENTS USED. 



The solution for absorbing carbon dioxide. The solution for absorbing 

 the carbon dioxide is prepared by dissolving 2400 grams of stick potassium 

 hydroxide in 1750 c. c. of water. After the solution becomes cold it is 

 decanted to remove all sediment, and the reservoir C is filled through the 

 tube at the top. This is best accomplished by inserting a 20 cm. length 

 of small-sized glass tubing in the open tube and attaching a funnel to it 

 by means of a short bit of rubber tubing. This elongated funnel con- 

 ducts the reagent well down into the chamber and avoids choking the 

 passage with the somewhat viscous liquid. The level of the liquid inside 

 and out should be essentially the same, the usual height being shown in 



