182 Prof. Tyndall on the Absorption and 



This Table shows the correctness of the foregoing surmise, and 

 proves that for small quantities of gas the absorption is exactly 

 proportional to the density. 



Let us now estimate the tensions of the quantities of gas with 

 which we have here operated. The length of the experimental 

 tube is 48 inches, and its diameter 2-4 inches ; its volume is 

 therefore 218 cubic inches. Adding to this the contents of the 

 cocks and other conduits which led to the tube, we may assume 

 that each fiftieth of a cubic inch of the gas had to diffuse itself 

 through a space of 220 cubic inches. The tension, therefore, of 

 a single measure of the gas thus diffused would be } t * th of 

 an atmosphere, — a tension capable of depressing the mercurial 

 column connected with the pump ^- 7 th of an inch, or about T jth 

 of a millimetre ! 



But the absorptive energy of olefiant gas, extraordinary as it 

 is shown to be by the above experiments, is far exceeded by that 

 of some of the vapours of volatile liquids. A glass flask was 

 provided with a brass cap furnished with an interior thread, by 

 means of which a stopcock could be screwed air-tight on to the 

 flask. Sulphuric ether being placed in the latter, the space 

 above the liquid was completely freed of air by means of a 

 second air-pump. The flask, with its closed stopcock, was now 

 attached to the experimental tube ; the latter was exhausted and 

 the needle brought to zero. The cock was then turned on so 

 that the ether-vapour slowly entered the experimental tube. 

 An assistant observed the gauge of the air-pump, and when it 

 had sunk an inch, the stopcock was promptly closed. The <ral- 

 vanometric deflection consequent on the partial cutting off of 

 the calorific rays was then noted; a second quantity of the 

 vapour, sufficient to depress the gauge another inch, was then 

 admitted, and in this way the absorptions of five successive 

 measures, each possessing within the tube 1 inch of tension, 

 were determined. 



In the following Table the first column contains the tensions 

 in inches, the second the deflection due to each, and the third the 

 amount of heat absorbed, expressed in the units already referred 

 to. For the purpose of comparison I have placed the corre- 

 sponding absorption of olefiant gas in the fourth column. 





Table III.- 



—Sulphuric 



Ether. 





Tensions ir 



l Deflections. 



Absorption. 



Corresponding absorption 



inches. 









bv olefiant pas. 



1 



64-8 



214 





90 



2 



70-0 



282 





123 



3 



720 



315 





142 



4 



73-0 



330 





154 



5 



73-0 



330 . 





163 



