462 PROFESSOR W. RAMSAY AND DR, S. YOUNG ON THE INFLUENCE OF 
sure whether evolved from and condensing to the solid or the liquid form. In accord¬ 
ance with these observations are former results of experiments on the vapour-pressures 
of ice and water, benzene, ethene bromide, acetic acid, cyanogen chloride, and carbon 
tetrachloride, all of which prove that in the passage of a substance from the solid to 
the liquid state no noticeable alteration in the curve of vapour-pressure occurs, but the 
curve preserves perfect regularity, both before and after the change.” 
4. In the following pages an experimental proof of the correctness of Professor 
Jas. Thomson’s theory will be given for camphor, benzene, acetic acid, and water. As 
these substances are representatives of very different chemical types, the law may be 
held to apply to all stable bodies in the liquid and solid states. 
5. From its high tension at the melting-point, camphor promised results which 
might be expected to throw light on this question. The experiment was performed 
as follows :— 
A barometer-tube was nearly filled with freshly distilled and filtered mercury, con¬ 
nected with a triple Sprexgel pump, and a vacuum established. The mercury was 
then boiled throughout the whole length of the tube, by heating it from below up¬ 
wards, with the flame of a Bunsen burner, so as to remove air and moisture. Dis¬ 
connecting from the pump, some fragments of previously fused pure camphor were 
placed on the surface of the mercury and kept in position by means of a coil of 
platinum gauze. The tube was again exhausted, and dry mercury was allowed to flow 
into the vacuous tube so as to cover the camphor and gauze. The tube was then dis¬ 
connected from the Sprengel pump, and inserted in a trough of dry mercury. By 
this means the entire absence of air and moisture was ensured, and the method is a 
more convenient one than that described in the paper which we had the honour to lay 
before the Society in June of last year, entitled, “ The Influence of Pressure on the 
Temperature of Volatilization of Solids” (Phil. Trans., 1884, p. 37). 
The experimental tube was heated by means of aniline-vapour. Having previously 
made a set of numerous determinations of the vapour-pressure of aniline at different 
temperatures, we were able, by regulating the pressure, to surround the barometer- 
tube containing the camphor with vapour at any desired temperature between 120° 
and 184° - 5. 
It is not here necessary to give detailed observations of the vapour-pressures of 
camphor at lower temperatures ; suffice it to say that they confirmed those obtained 
by this, and by another method described in the paper already referred to. For the 
purpose of this memoir we shall confine ourselves to pressures at temperatures near 
the melting-point. 
6. The results were calculated according to the formulae :— 
P' = B— [b —/3— (/X 0 - 00018 L x }> and 
P=P' —(P'xO-000169 f) = (P'-P'lhf for t = 20°^j 
P=Pi ’essure of vapour in millimeters of mercury, reduced to 0°. 
