G8 
PROFESSOR W. RAMSAY AND DR. M. AY. PRAYERS 
T„, T„', &c. ; and by reference to tables, the absolute temperatures T^, T//, &c., for 
some standard substance, such as water or methyl alcohol, corresponding to the same 
pressures, are found. The ratios T„/T 4 , T„7T/, &:c., are then calculated, and are plotted 
on curve-jmper against the temperatures T^, Tj', &c., as ordinates. The points so 
obtained should lie on a straight line, and the temperature corresponding to anv 
particular vapour-pressure can be discovered by multiplying the absolute temperature 
corresponding to that pressure for the standard substance by the value of the ratio 
corresponding to that temperature which is read from the line. 
For example ;—the following result was obtained with krypton— 
Pressure. 
T„ (krypton). 
TDCHSOII). 
Ta/Ti. 
millims. 
Abs. 
Abs. 
385 • 6 
112-7° 
321-8° 
0-3502 
898-7 
123-1 
342-3 
0-3596 
11970-0 
170-9 
429-3 
0-3981 
28800-0 
197-9 
471-4 
0-4193 
If, now, it is recpiired to calculate the boiling-point of krypton at 760 millims., the 
ratio is plotted against the values of 17, and the value of the ratio correspondijig to 
the temperature 338° (the boiling-point of methyl alcohol at normal pre.ssure), is read 
from the line. It is 0'3578 ; and the product 0'3578 X 338° is the boiling-point of 
krypton on the absolute scale, 120‘9° abs. 
Tills relation is expressed Iiy the formula given by Ramsay and Young :— 
Ty'T, = T;/Td - c(T„ - T,/). 
The value of c, it vdll be noticed, is constant for each pair of substances ; and if 
referred to a .standard such as methyl alcohol, the ratio bet^veen the values of c for 
various gases has a physical meaning; this vdll be considered later. 
The temperatures were based on measurements made vdth a Callexdar's com¬ 
pensated con.stant-pressure hydrogen thermometer (‘ Hoy. Soc. Proc.,’ vol. 50, p. 247); 
in certain cases, a platinum-resistance thermometer, rvorked in conjunction with a 
Callendar’s recorder, vms used ; it had been standardised by help of the hydrogen 
thermometer ; in others, the hydrogen thermometer was directly employed. 
For low pressures, an apparatus v’as used, the arrangements of vchich are shown 
in tlie annexed tigui'e (tig. 5). 
The gas vms introduced liy means of the inverted siphon into the tube-reservoir a : 
this reservoir was in communication v’ith the small Inilb h, u hich in its turn was con¬ 
nected with the pre.ssure-gauge c, and with a Topler’s pump through the stop-cock d ; 
the bulb could be cooled by means of one of the devices previously alluded to. After 
evacuating the bulb, gauge, and connecting-tubes, the gas was introduced through 
