138 
POPULAR SCIENCE REVIEW. 
and they utterly collapsed under the chemical scrutiny of Dr. 
Flight. 
It has been well said with reference to other subjects that 
* the failures of the past prepare for the triumphs of the future/ 
Nor is this saying inapplicable to our would-be diamond manu- 
facturers. Scarcely had Mr. Mactear’s investigations faded 
from the public mind, when Mr. A. H. Allen, of Sheffield, put 
in a claim on behalf of Dr. R. S. Marsden ; and before this 
second process is revealed, Mr. J. Ballantine Hannay, a young 
Glasgow chemist, steps forward and actually places in our hand 
an artificial diamond ! 
For some time past Mr. Hannay has been engaged in a 
most interesting series of researches which have unexpectedly 
led up to the present discovery. To appreciate these researches 
it is necessary to turn to a subject which appears, at first sight, 
to have no bearing whatever upon the artificial production of 
the diamond. 
More than half a century ago, Cagniard de la Tour made 
some remarkable experiments to determine the effect of heat 
upon liquids closely sealed in strong tubes. This inquiry was 
afterwards followed up by Dr. Andrews, of Belfast. He showed, 
for example, that carbonic acid gas above a certain temperature 
cannot be liquefied by means of pressure ; but the gas, if com- 
pressed, assumes a condition which is neither that of a liquid 
nor that of a gas. Let the . temperature be lowered, and it 
becomes a true liquid. Let the pressure be lowered, and it 
becomes a true gas. It was found that the two physical states 
of liquidity and gaseity pass by insensible transition one into the 
other ; the continuity between the two conditions being perfect* 
That particular temperature, above which pressure does not 
produce liquefaction, is termed the critical point. 
Reverting to the experiments of Cagniard de la Tour and 
Andrews, in which liquids were heated in closed tubes, let us 
suppose a solid to be dissolved in the liquid, and the solu- 
tion to be then raised beyond its critical point. What will 
occur ? The liquid will pass into the gaseous condition ; but 
what will become of the solid ? This is the question which 
Mr. Hannay, working in conjunction with Mr. Hogarth, 
sought to answer. At first sight it might be fairly assumed that 
if the solid were not volatile at the temperature to which it 
was exposed, it would be incapable of assuming the gaseous 
condition, and that it would therefore be abandoned by the 
solvent : hence, when the menstruum passed through the 
critical state, and became gaseous, the dissolved body would be 
precipitated in a solid form. 
Such an assumption, however, was flatly contradicted by 
experiment. It was soon found that in many cases the solid 
