102 REPORT— 1886. 



whicli in each gas Boyle's law is found to be, though appi'oximatelj true 

 for small variations of pressure, deviated from more and more as the 

 pressure is increased (' Memoires de I'Academie,' t. xxvi.). 



Some of the gases which Regnault selected were liquefied at the 

 temperature of the experiment by pressure alone, and in these cases it 

 was noticed that drops of liquid condensed on the mercury and on the 

 glass, and that while this was taking place quite a considerable diminu- 

 tion of volume was brought about by a small and gradual increase of 

 pressure (p. 261). The liquefaction of these gases — viz., H2S, SO2, 02^,2, 

 NH3, CO2, and of chlorine and hydrogen chloride — was known, having 

 been effected by Faraday many years before.' 



Andrews has shown ^ that a body in the gaseous state may be 

 brought to the liquid state by a continuous process, in which it is im- 

 possible to notice any precise point at which the gas becomes liquid, the 

 deviations from Boyle's law, which are hardly noticeable at first, being 

 gradually increased till the relation between pressure and volume is 

 not even approximately repi'esented by this law, the gas becoming on 

 still continued j^ressure less and less compressible, so as to finally be 

 undistinguishable in this respect from a liquid. It was thus shown 

 incidentally in the course of Andrews' expei'iments that for high pres- 

 sures the gases examined became less compi-essible the greater the 

 pressure, a phenomenon which was observed by Regnault for hydrogen 

 only, but not for the other gases at the pressures to which he subjected 

 them, i.e. up to 30 atmospheres. 



Before Andrews, Natterer had made experiments extending over a 

 long time — his published papers dating from 1844 to 1856 — with the 

 object of liquefying and solidifying gases by great pressures, and he 

 found that up to 2790 atmospheres the gases hydrogen, oxygen, nitrogen, 

 nitric oxide, as well as atmospheric air, beyond 100 atmospheres, were all 

 notably less compressible than Boyle's law required. ^"^ The general result 

 of the effect of pressure on volume in the case of gases at ordinary tem- 

 peratures as given by Regnault and by Natterer made it desirable to in- 

 vestigate this relation with all the accuracy attainable for a range of 

 pressures much greater than Regnault had been ahle to measure with 

 sufficient accuracy. 



Amagafs Investigations on Relation of Pressure to Volume in Gases. 



Amagat in the year 1880 published a paper, the first of a series, in 

 which he examined air, hydrogen, oxygen, carbon monoxide, marsh-gas, 

 and ethylene as to their behaviour at given temperature at various pres- 

 sures up to 400 atmospheres or beyond.'' 



In these investigations Amagat obtained his greatest pressures by the 

 height of a column of mercury in narrow flexible steel tubes attached to 

 the side of a shaft of a mine of some hundreds of metres in depth. 



' Phil. Trails. 182.'5, pp. 160, 189. 



2 Phil. Trans. 1869, Part II. p. 575. 



= PoggendorfE's Annulen, Ixii. 1844, p. 132, and Liebig'.s Ann. liv. 1845 p. 254. 



■• Sitzim/f slier ichte der Miserlic/ien Akademic der Wissenschaften zu Wien, v. 1850, 

 p. 351 ; vii. 1851, p. 557; xii. 1854, p. 199. 



' Poggendorff's Atinale/i, xciv. 1855, p. 436. 



« Annates de Chiinie et de Physique, 1880 (5), xix. p. 345 ; 1881 (5;, xxii. p. 353 ; 

 1883 (^5), xxviii. pp. 456, 480, 501. 



