ON NITROUS OXIDE IN THE GASKOUS AND LIQUID STATES. 211 



tbe thermometers in this shaft (which was dry) has vitiated the observations, 

 the instruments employed being maximum thermometers. Two of the slow 

 non-registering thermometers mentioned in last year's lleport have been 

 sent to M. Delesse, to be used for verification. 



The slow- action thermometers are constructed on the foUo'ndug plan : — • 

 The bulb is cylindrical and very strong, and is surrounded by stearine or 

 tallow, which fills up tlic space between it and a strong glass shield in 

 which the thermometer is inclosed. The shield is not hermetically sealed 

 (not being intended for protection against pressure), but is stopped at the 

 bottom with a cork, so that the thermometer can be taken out and put in 

 again if desired. Stearine and tallow were selected after trials of several 

 substances, including paraffin-wax, bces'-wax, glue, plaster of Paris, pounded 

 glass, and cotton-wool. The thermometers are inclosed in copper cases 

 lined with india-rubber. When placed, without these cases, in v/ater dif- 

 fering 10° from their own temperature, they take nearly half ti minute to 

 alter by one tenth of a degree. 



In concluding this Eeport, your Committee desire to express their regret 

 at the losses which they have sustained by the deaths of Prof. Phillips, Sir 

 Charles Lyell, and Col. Strange, of whose valuable services they liavo been 

 deprived -flithin the last three years. 



Nitrous Oxide in the Gaseous and Liquid States. 

 By W. J. Janssen. 



[A communication ordered by the General Committ.ee to be printed in e.vlenso.'] 



The experiments of Faraday on the liquefaction of gases have already proved 

 that gases at the ordinary conditions of pressure and temperature are vapours 

 at a remote stage from their points of condensation. If several gases sub- 

 mitted to great pressure and the cold of the carbonic acid and ether bath 

 did not exhibit any appearance of liquefaction, the cause is probably that 

 Faraday did not obtain a temperature low enough to produce liquefaction. 

 Hence we may conclude that the gaseous and liquid states of matter depend 

 only on the temperature and pressure to which it is exposed. The interest- 

 ing experiments of Dr. Andrews with carbonic acid (Philosophical Trans- 

 actions for 1869) not only verified this conclusion, but gave the important 

 result that gases and liquids are distant stages of the same condition of 

 matter, which may pass into one another without breach of continuity. The 

 temperature at which matter, without sudden change of volume or abrupt 

 absorption of heat, passes from the ordinary liquid to the ordinary gaseous 

 state is called by Dr. Andrews the critical point ; above that temperature a 

 gas never can be liquefied by pressure, it behaves like a permanent gas ; 

 below that temperature it will be liquid or gas, or more exactly liquid or 

 vapour, according to the pressure to which it is exposed. For the details I 

 refer to the above-mentioned paper. 



I have made the same kind of experiments with nitrous oxide, a gas whoso 

 physical properties agree much Avith those of carbonic acid. The apparatus 

 was similar to that used by Dr. Andrews, to whom I am much indebted for 

 the great kindness with which he has afforded me every instruction, and for 

 his invaluable advice about tlie use of Lis apparatus during my stay at Belfast 

 and afterwards. 



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