100 REPORT — 1886. 



First Report on our Experimental Knowledge of the Properties of 

 Matter tuith respect to Volume, Pressure, Temperature, and 

 Specific Heat. By P. T. Main, M.A. 



Belation of Pressure to Volume ; Oases — Regnaulfs Investigations, and 



General Besults. 



Before Regnanlt published his ' Memoires ' attempts Lad been made- 

 without success to detect deviations from the relation of pressure to- 

 volume required by Boyle's lavr. In his sixth memoire ' of tome sxi. 

 Rewnault describes in detail his arrangement for testing the accuracy of 

 Boyle's law for atmospheric air, and for the gases nitrogen, carbon 

 dioxide, and hydrogen. At a large number of pressures ranging fi'om. 

 that of a single atmosphere to that of about thirty atmospheres experi- 

 ments were made of the following kind : a manometer, at the middle of 

 which was etched a mark which divided it into (almost) exactly equal 

 volumes, as known by the weights of its contents of mercury, was 

 filled at a given exactly known temperature and pressure with atmo- 

 spheric air, or the gas to be examined ; the pressure was then increased 

 until the mercury was forced up to the manometer tube, so that the top 

 of the meniscus was seen, by the cathetometer, to be just touched by the 

 mark on the middle of the manometer tube, the length of which was 

 about 3 metres ; the pressure was then again recoi-ded, and the ratio of 

 the foi-mer to the latter pressure calculated. If in all cases Boyle's law 

 applied with accuracy the ratio would always be 2 to 1. But it was 

 found for the gases mentioned that this was never accurately the case, 

 and that the deviation from this ratio was greater the greater the origi- 

 nal pressure, and that air and nitrogen under these conditions up to 'SO- 

 atmospheres were always more compressible than Boyle's law required,, 

 but that for hydrogen the compressibility was always Jess than Boyle's 

 law required, and that the deviations from Boyle's law were always 

 greater the greater the original pressure up to 30 atmos. 



For example, in the case of nitrogen the ratio of vp for, the original 

 and for the doubled pressure (which should be 1, if Boyle's law applied, 

 exactly) was 



1-001012 for original pressure 753"96 mm. 

 and 1-006784 „ „ 10978-20 „ 



the temperature beiug constant (4° to 5°) in each case. 

 Again, for carbon dioxide the ratio was 



at 3-08° 1-007597 for original pressure 764-03 mm. 



and, at 2-7° 1-1.53681 „ „ 9612-39 „ 



But for hydrogen the ratio was 



at 4-4° 0-998584 for original pressure, 969-19 mm. 



and, at 8-95° 0-994460 „ „ 1183-06 „ 



In all three cases we notice that the deviation from Boyle's law i& 

 o-reater the greater the pi-essure ; the deviation is much gi-eater for carbon 

 dioxide than for the other two gases ; for hydrogen the compressibility is- 

 less, for the others greater, than if Boyle's law were accurate. These. 



■ Mcmnires cle VAcaicmie, t. sxi. 



