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POPULAR SCIENCE REVIEW. 
scales, resembling graphite. Such scales are known to work- 
men under the curious name of kish. 
Every schoolboy knows now-a-days that carbon occurs in 
nature crystallized as two entirely distinct minerals : in the 
one form it is known as graphite , plumbago , or black lead ; in 
the other form as diamond. Metallurgists, as just stated, are 
familiar with the artificial production of graphite, and this 
body has also been produced by certain chemical reactions ; 
but the artificial crystallization of carbon in the form of 
diamond has heretofore invariably baffled the chemist. 
While the air of Glasgow was filled with the rumours of 
Mr. Mactear’s experiments, it was natural to turn to Messrs. 
Hannay and Hogarth’s researches, if haply their new method 
of gaseous solution might lead us to the desired end. They 
found that when a solid is freed from its gaseous solvent, it is 
invariably deposited in a crystalline condition. Now, if carbon 
could be thus dissolved, there was, of course, the bare pos- 
sibility that it might be deposited in the crystalline form of 
diamond. 
On applying himself to this inviting problem, Mr. Hannay 
was disappointed to find that all the forms of carbon with 
which he experimented, such as graphite, or charcoal, or 
lamp-black, obstinately refused to yield to any of the solvents 
which he brought to the attack. It was clear, therefore, that if 
the problem was to be solved at all it must be solved in an 
indirect manner, and Mr. Hannay’s ingenuity was equal to the 
occasion. 
Carbon is remarkable for the multitude of volatile com- 
pounds which it is capable of forming with hydrogen. Now 
Mr. Hannay found that when a gas containing carbon and 
hydrogen is subjected to heat under great pressure in the 
presence of certain metals, such as magnesium or sodium, the 
hydrocarbon is broken up, and its hydrogen combines with the 
metal, while its carbon is set free. In order to command the 
high temperature and the intense pressure necessary for this 
reaction, Mr. Hannay employs wrought-iron tubes, about 3J 
inches in thickness, and yet these are frequently torn open in 
the course of the experiments. 
It appeared probable that the carbon set free in this decom- 
position might, at the moment of its formation, or when in the 
nascent condition, be dissolved by the gas, and then, on a 
reduction of pressure, be precipitated in a crystalline condition. 
Mr. Hannay has found that in order to obtain the carbon in the 
required crystalline state it is necessary that a stable 
compound containing nitrogen be present. When these 
conditions were fulfilled, the operator had the satisfaction of 
