PROCEEDINGS 
OE THE 
ROYAL SOCIETY OF EDINBURGH. 
vol. xiii. 1884-85. No. 120. 
Monday, 20 th April 1885. 
ROBERT GRAY, Esq., Vice-President, in the Chair. 
The following Communications were read :■ — 
1. Effect of Pressure on the Temperature of Minimum Com- 
pressibility of Water. By Professor Tait. 
2. Note on the Variation by Pressure of the Melting-Point 
of Paraffin, &c. By W. Peddie, Esq. Communicated 
by Professor Tait. 
As the result of Andrews’ experiments on the boiling-points of 
substances, we have the law enunciated that There is a critical 
temperature for every vaporous or gaseous substance ; such that, 
only when its temperature is below this, can the substance be 
reduced to the liquid form by any pressure, however great. 
Similarly, a law may be laid down regarding the passage from the 
liquid to the solid state, or vice versa. Thus we may say that 
There is a critical temperature for every solid substance, which 
contracts in the act of liquefaction, such that only when its temper- 
ature is above this, can the substance be reduced to the liquid form 
by any pressure, however great ; and for every liquid substance, 
which contracts in the act of solidification, such that only when 
its temperature is below this, can the substance be reduced to the 
solid form by any pressure, however great. 
There is as yet no experimental evidence for this law, but I hope 
VOL. xm. 
M 
