78 Royal Society: — Dr. Andrews on the Physical 



" Preliminary Notice of further Besearches on the Physical Pro- 

 perties of Matter in the Liquid and Gaseous States under varied 

 conditions of Pressure and Temperature." By Dr. Andrews, F.E.S. 



The investigation to which this note refers has occupied me, with 

 little intermission, since my former communication in 1869 to the 

 Society, " On the Continuity of the Liquid and Gaseous States of 

 Matter." It was undertaken chiefly to ascertain the modifications 

 which the three great laws discovered respectively by Boyle, Gay- 

 Lussac, and Dalton undergo when matter in the gaseous state is 

 placed under physical conditions differing greatly from any hitherto 

 within the reach of observation. It embraces a large number of 

 experiments of precision performed at different temperatures and 

 at pressures rangiug from twelve to nearly three hundred atmo- 

 spheres. The apparatus employed is, in all its essential parts, 

 similar to that described in the paper referred to ; and so perfectly 

 did it act that the readings of the cathetometer, at the highest 

 pressures and temperatures employed, were made with the same 

 ease and accuracy as if the object of the experiment had been 

 merely to determine the tension of aqueous vapour in a barometer- 

 tube. In using it the chief improvement I have made is in the 

 method of ascertaining the original volumes of the gases before 

 compression, which can now be known with much less labour 

 and greater accuracy than by the method I formerly described. 

 The lower ends of the glass tubes containing the gases dip 

 into small mercurial reservoirs formed of thin glass tubes, which 

 rest on ledges within the apparatus. This arrangement has pre- 

 vented many failures in screwing up the apparatus, and has given 

 more precision to the measurements. A great improvement has 

 also been made in the method of preparing the leather-washers 

 used in the packing for the fine screws, by means of which the 

 pressure is obtained. It consists in saturating the leather with 

 grease by heating it in vacuo under melted lard. In this way the 

 air enclosed within the pores of the leather is removed without 

 the use of water, and a packing is obtained so perfect that it 

 appears, as far as my experience goes, never to fail, provided it 

 is used in a vessel filled with water. It is remarkable, however, 

 that the same packing, when an apparatus specially constructed 

 for the purpose of forged iron w T as filled with mercury, always 

 yielded, even at a pressure of 40 atmospheres, in the course of a 

 few days. 



It is with regret that I am still obliged to give the pressures in 

 atmospheres as indicated by an air- or hydrogen-manometer, with- 

 out attempting for the present to apply the corrections required 

 to reduce them to true pressures. The only satisfactory method 

 of obtaining these corrections would be to compare the indications 

 of the manometer with those of a column of mercury of the requi- 

 site length; and this method, as is known, w T as employed by 

 Arago and Dulong, and afterwards in his classical researches 

 by Begnault, for pressures reaching nearly to 30 atmospheres. 

 Tor this moderate pressure a column of mercury about 23 metres, 



