Relations of Liquids and their Saturated Vapours. 95 



measured at t temperatures, are proportional to the h tangents 

 (§4) respectively. 



§ 39. To find this tangent, we take two points in the line of 

 vapour (Plate I.), and measure by scale, first the difference 77 of 

 the ordinates at those points, and second the difference 6 of the 



temperatures. The quotient - = h. Thus the easy plan is to 



select the points so that t\ = 1, which gives 6 = h, the constant of 

 that particular line of vapour. 



§ 40. As a convenient point through which to draw the line 

 parallel to the axis upon which r temperatures have to be mea- 

 sured, we may take the intersection of the muriatic-ether-line 

 with 0° C. This is drawn on Plate III. It intersects the hy- 

 drobromic-ether-line at 27°*4. The vapour- density of this ether 

 is 54*5 (on hydrogen scale), and spec. grav. at 0° 1*473; the 

 volume at 27°*4 by Pierre's observations is 1*0387 (volume at 0° 

 unity). Hence, to rind the liquid molecular volume at 27°*4, the 



u + ', 54*5x1*0387 ,. , 

 t temperature, we nave to compute TTJ/ro » which comes 



out 38*43=/* of hydrobromic ether. 



The hydriodic-ether-line intersects the t line at 62°*4, at which 

 temperature the volume is 1*082; the vapour-density is. 78, and 



spec. grav. at 0° 1*975; we have — t^qjz — = 42*73 = ^ of hy- 



driodic ether. 



Now h of the first is 158*6, and of the second 177 (as may be 

 computed from the chart, Plate I.) . These are in the same ratio 



as the respective values of \x. Thus =4*12, and . „ = 4*14, 



that is, — = a constant. 



The t temperature of the muriatic ether is 0°, spec. grav. 0*920, 

 vapour-density 32, and h = 144; hence to find ^ we have 



32 nA „ ^h 144 



— — - =34*78, and - = =4*14, the same as the preceding. 



Chloroform intersects the r line at 51°*4, where the volume 

 by Pierre is 1*0664, vapour-density 60, spec. grav. at 0° 1*525, 

 h=17l : to find jjl, there is 



60 x 1*0 664 h 171 ^ AQ 



^^ — - =41*96, and - = 7^7^ =4*08. 



1*525 ' fju 41*96 



The mean of these four values of - is 4*11. 



§ 41. By inspecting fig. 1 it will be seen that measuring the 

 temperatures on the r line implies that the absolute temperatures, 



