ARTIFICIAL DIAMONDS. 
139 
body was not deposited, but remained in a state of solution or 
diffusion in tbe gas. We are tbus brought in contact with the 
unexpected phenomenon of a solid substance being dissolved by 
a gas , just as it might under ordinary circumstances be dis- 
solved by a liquid. 
Since water is the most generally useful solvent, it might 
be supposed that such experiments would be best made with 
aqueous solutions. Practically, however, the use of water is 
precluded, on account partly of its inconveniently high critical 
point, and partly of the fact that water at a high temperature 
and under great pressure is capable of exerting a corrosive 
action upon the glass tubes in which the experiments are 
undertaken. A more convenient solvent was found in alcohol, 
and many of the early experiments of Messrs. Hannay and 
Hogarth were made with a solution of iodide of potassium in 
this menstruum. A strong tube was about half filled with an 
alcoholic solution of potassic iodide ; the extremity was sealed, 
the tube placed in an air-bath and heat applied. Having 
passed through the critical stage, the alcohol became gaseous ; 
but the iodide, instead of being precipitated, remained in 
solution in this gas. Even when the temperature rose to 
380° C., or about 150° above the critical point, tbe alcohol-gas 
still asserted its solvent power over the solid salt. Moreover, by 
an ingenious arrangement, if became possible to expose a frag- 
ment of the iodide to the action of the gas without allowing it 
ever to come in contact with the liquid ; yet the solid slowly 
disappeared, and was at length completely dissolved by the 
invisible solvent. But on rapidly releasing the gaseous solution 
from the pressure to which it had been exposed, the iodide was 
precipitated, either as a cloud of delicate snow-like crystals, or 
as a crystalline film, like hoar-frost, on the inside of the glass 
tube. On again increasing the pressure, however, the crystals 
were re-dissolved, and once more disappeared. 
Here then a new light broke in upon the phenomenon of 
solution. Hitherto it had been supposed that only liquids 
possessed solvent powers, but Messrs. Hannay and Hogarth 
have now shown that gases also are similarly endowed. In 
short, these researches fortify tbe conclusion which Hr. 
Andrews had previously reached, that there is perfect con- 
tinuity between the liquid and the gaseous conditions. 
If such extraordinary solutions can be effected, what more 
natural than to inquire whether carbon could be caused to 
dissolve in some appropriate solvent P Carbon is a remarkably 
obstinate body, resisting all ordinary menstrua, such as acids 
and alkalies, alcohol and ether. It is worth noting, however, 
that molten cast-iron can dissolve carbon ; and that when the 
metal cools the carbon is partially separated in crystalline 
