2~8 Prof. Tyndall on the Absorption and 



The following results were afterwards obtained. I may remark 

 that a subsidiary gauge wa3 used, so as to prevent the destruc- 

 tive gases from entering the air-pump. 



Absorption. 



Chlorine 15 inches ....... 32 



Chlorine 14 inches 30 



Chlorine 14 inches ...... 30 



Hydrochloric acid 14 inches . , . 47 



Chlorine again 30 



Hydrochloric acid ..:•••• 56 



In all cases the effect of the compound gas was found to 

 exceed that of the elementary one ; so that the chemical change 

 which renders chlorine more transparent to light renders it more 

 opake to obscure heat. 



Great care is required in experiments on hydrochloric acid, 

 and great care was bestowed on the above. Previously to the 

 introduction of the gas the experimental tube was filled with 

 perfectly dry air, so as to leave a perfectly dry residue on ex- 

 haustion. The gas was allowed to stream through the drying- 

 tube until all traces of air were expelled; then a joint was sud- 

 denly broken^ and the retort was connected with the experi- 

 mental tube. The gas thus passed directly from the retort 

 through the drying-apparatus into the vacuum. It was difficult 

 to avoid sending in with the gas a few particles of moisture ; 

 but these, if such existed, appeared to be dissipated by the dy- 

 namic heating of the gas on entering the tube, and kept dissi- 

 pated by the flux of heat passing through it, At all events the 

 closest scrutiny could detect no trace of mist or turbidity within 

 the tube; it was perfectly transparent throughout. The chlo- 

 rine, on the contrary, was intensely coloured. 



I made many experiments with chlorine which had been col- 

 lected over water, but something (what, I know not yet) appeared 

 to be in all cases carried along with the gas from the water into 

 the tube, which materially augmented its absorption. 



The above experiments were made in the early part of this 

 inquiry, and before I had become aware of all the peculiarities of 

 my apparatus. Subsequent experiments reduced in some degree 

 the absorption both of chlorine and hydrochloric acid. Very 

 careful experiments made on the 29th of October gave the fol- 

 lowing absorption for these two gases, at a tension of 30 

 inches : — 



Chlorine 39 



Hydrochloric acid . . 53 



The chlorine and hydrochloric acid were removed from the 

 experimental tube in the following manner : — A cock and con- 



