M. R. Bunsen on the Law of Absorption of Gases. 123 



mined by the small thermometer c. The upper end of the outer 

 cylinder is closed by an iron lid having a hinge at one side, and 

 fastened down by means of a nut and screw attached to the iron 

 rim h, fitting into a small slit in the side of the lid. In the 

 middle of the cover inside there is a raised rim of iron, over 

 which a thick sheet of caoutchouc is extended and fastened by a 

 screwed ring s. This distended caoutchouc serves as a spring 

 against which the top of the tube can be pressed, keeping it in 

 a fixed position during the violent agitation necessary in the 

 process of absorption. 



The experiment itself is conducted in the following manner: — 

 A volume of the gas to be examined is first collected in the tube 

 over mercury, and the usual precautions taken in reading off, 

 &c, as in the reduction and measurement of gases. A measured 

 volume of water freed from air is next admitted under the mer- 

 cury into the tube, which is then screwed tightly against the 

 caoutchouc plate, and the tube thus closed placed in the cylin- 

 der containing some mercury, and over that a quantity of water. 

 As soon as the pressure within and without has been equalised 

 by slightly turning the tube, it is again closed, and the whole 

 apparatus rapidly agitated for about a minute. This agitation, 

 with opening and closing of the tube, is continued many times, 

 until no further change of volume is perceptible. The observa- 

 tions necessary for the measurement and reduction of the residual 

 gas are then made. Besides the temperature t and the baro- 

 metric pressure p, four readings from the divided tube are re- 

 quired : — 



1. The lower surface of mercury in the outer cylinder at a. 



2. The upper surface of mercury in the absorption-tube b. 



3. The upper surface of water in the absorption-tube at c. 



4. The upper surface of water in the outer cylinder at d. 



The method of calculation will be best explained by an example. 

 I select for this purpose an experiment on the determination of 

 the absorption-coefficient of nitrogen and water at 19° C. 



Elements of the Calculation. 

 1 . Observations before the Absorption. 



Lower surface oi mercury in outer cylinder a = 423'6 millims. 



Upper surface of mercury in tube* . . 6 = 124 , 1 ... 



Barometric pressure p = 746 , 9 



Temperature of the absorptiometer . . / = 19 0, 2C. 



Temperature of the barometer . . . . t = 19 o, ... 



* In this experiment the absorptiometer contained only mercury, and 

 no water. 



