280 Prof. Tyndall on the Absorption and 



§ 4. In the following Table is given the absorption of a 

 number of gases at a common tension of one atmosphere. 



Table I. 



Name. Absorption. Name. Absorption. 



Air 



Oxygen . . . . . 1 



Nitrogen 1 



Hydrogen 1 



Chlorine 39 



Hydrochloric acid . . 62 



Carbonic oxide ... 90 



Carbonic acid . . 

 Nitrous oxide • . 

 Sulphuretted hydrogen 

 Marsh-gas 

 Sulphurous acid . . 

 Olefiant gas . , . 

 Ammonia .... 



90 

 355 

 390 

 403 

 710 

 970 

 1195 



Air, oxygen, nitrogen, and hydrogen are all set down as equal 

 to unity in the above Table. I do not mean thereby to affirm 

 that there are no differences between these gases as regards their 

 powers of absorption, but that the most powerful and delicate 

 tests which I have hitherto applied have failed to establish a 

 difference in a satisfactory manner. It is not improbable that 

 the action of these gases may turn out to be less even than I have 

 found it. For who can say that the best-constructed drying- 

 apparatus is really perfect ? Besides, stopcocks must be greased, 

 and hence may contribute an infinitesimal impurity to the air 

 passing through them. I cannot even say that sulphuric acid, 

 however pure, may not deliver a modicum of vapour to the cur- 

 rent of air passing through it. At all events, if any further 

 advance should be made in the purification of the gases, it will 

 certainly only tend to augment the enormous differences exhi- 

 bited in the above Table. 



Ammonia, of the tension mentioned, stands highest in the 

 above list as regards absorptive energy. I believe that a length 

 of less than 3 feet of this gas, which to the vision is as trans- 

 parent within the tube as the vacuum itself, is perfectly black to 

 the rays emanating from the source here made use of. When 

 the gas was in the tube, the interposition of a double metallic 

 screen between the pile and source augmented the deflection 

 very slightly. But I shall show, further on, that the ammonia 

 in this experimeut could not exhibit the full energy of its absorp- 

 tion, and that the length indicated is in all probability abso- 

 lutely impervious to the heat issuing from our source. 



It would be a mere affectation of accuracy to try to deal with 

 smaller quantities of the first four substances mentioned in the 

 Table than those with which I have here operated. Still, if 



rays. An opake solution of iodine in bisulphide of carbon behaves simi- 

 larly. The details of these experiments shall be published in due time : 

 they were publicly shown in my lectures many months ago. — June 13, 1862. 



