Relations of Liquids and their Saturated Vapours. 87 



ture reckoned from —274°; the sixth root of the quotient was 

 computed and laid off by scale as ordinate to the temperature : 



e.g. steam at 100°, pressure 760 millims., < s~t r 6 =1*1254 is 



the ordinate which in Plate I. is laid off to a scale of 13^ inches 

 to unity, the scale of temperature being 10 inches to 100°. 



§ 17. The straight line WATER passes through the points 

 thus computed from the pressures at 30°, 40°, 50°, 60°, 70°, 

 and 100° of Regnault's courbe graphique. It is continued 

 downwards in Plate II. to the axis of temperature, which it cuts 

 at — 79 c . The chart-lines of equal pressure, from 10 to 1 millims., 

 have been laid down, so that the divergence from the straight 

 line may be properly estimated at the lower part of the range. 

 The maximum divergence, it will be seen, does not exceed -^q of 

 an inch of mercury. This straight line produced downwards 

 cuts the ordinate of —274° in 1*226. 



§ 18. The next to examine is the line marked alcohol on 

 Plate I. It will be remarked that the accordance is very com- 

 plete. It is continued downwards in Plate II., and is found to 

 cut the axis of temperature at — 82°*7, being 3°*7 lower than 

 the water-line. 



§ 19. There are nine sets of points in Plate II., marked 

 S« 0^ + 18(110^), &c, which are obtained from Regnault's 

 observations of pressure of vapour from nine hydrates of sul- 

 phuric acid*. A straight line was drawn through each set, using 

 a short straight edge ; and this was afterwards produced down- 

 wards to cut the axis of temperature : thus was obtained an un- 

 biased representation of the convergence of the lines as the 

 means of estimating the probability of their cutting the axis 

 at the same point as water. The boiling-point of the hydrate 

 SwO"^, 3(HO*) was found to correspond with the line drawn on 

 the chart produced upwards to 171°. 



§ 20. The next step was to compute by simple proportion 

 from the slope of each line the point where it intersects the ordi- 

 nate at —274°. These were laid off and the lines drawn as 

 shown in Plate III. The remarkable convergence towards one 

 point at —274°, shown in this Plate, is thus a result quite un- 

 biased by any anticipation. The computed value of zn of the 

 mercury-line is 0*803, and of the sulphur-line 0*799 • the values 

 for the other lines run between 0776 and 0*843, except the sul- 

 phide-of-carbon. The water-line cuts it at 1*226, two- thirds of 

 which is 0*817. This is where the lines of muriatic ether and 

 sulphuric ether intersect, and is a fair average of the best of the 

 others. The dynamic series of sulphurous acid point to the 



* Annates de Chimie et de Physique, vol. xv. p. 174. 



