118 



Mr. G. Ansdell on the 



[Jan. 29, 



pumps for the liquefaction of gases. The tensions of the saturated 

 vapour then obtained were so entirely different from M. Cailletet's 

 results, that it appeared to me to be possibly due to a slight impurity 

 in the gas, probably a trace of mono-bromethylene which always occurs 

 in the red copper compound of acetylene, and is very difficult to 

 completely eliminate. 



I therefore prepared a quantity of the silver compound (which can 

 be obtained entirely free from mono-bromethylene) by passing acety- 

 lene prepared in the same way as formerly f viz., by the action of 

 alcoholic potash on di-bromethylene, into an ammoniacal solution of 

 nitrate of silver. 



On filling several tubes with acetylene generated by the action of 

 hydrochloric acid on this compound, the .tensions were found to be 

 exactly the same as those obtained with the acetylene made from the 

 copper compound, thus proving the correctness of the former experi- 

 ments. 



As the Cailletet pump is so well adapted to the examination of 

 gases in their liquid state, and is at the same time so easily managed, 

 it appeared interesting to determine the physical constants of some 

 other gases, and Professor Dewar suggested an examination of the 

 halogen acids, with regard to their physical relations to each other, 

 more especially as we have absolutely no reliable knowledge as to 

 these numbers. 



Faraday was the first to liquefy hydrochloric acid gas in 1823, and 

 he subsequently, in 1848, made a series of determinations of the vapour 

 tensions of the liquid at different temperatures. He also liquefied 

 hydrobromic and hydriodic acids, but gives no account of their pro- 

 perties in a liquid state. Grore (" Proc. Roy. Soc," vol. xiv), 

 examined very carefully the chemical properties of liquid hydrochloric 

 acid, its solvent action, &c, but made no determinations of its 

 physical constants. 



Hydrochloric acid is the only one I have as yet had time to examine, 

 with the following results :' — 



The gas was made by the action of strong sulphuric acid on dry 

 chloride of ammonium, being afterwards freed from sulphuric acid 

 and dried before entering the tubes. It was found of no advantage 

 to continue the stream of gas for more than six hours, as a constant 

 minimum of air always remained in the tube at the end of this time 

 (about 473-oth of the total volume of the tube) which it appeared utterly 

 impossible to remove. 



The pump was used in the same way as described in my former 

 paper, two iron reservoirs being used, one containing the air mano- 

 meter, and the other the tube with the gas to be liquefied. 



Apart from the mere determination of the vapour tensions, densi- 

 ties, &c, the ratio of the volume of saturated vapour to that of the 



