445 
of carbon and hydrogen, &c. 
for the preparation of this substance only, is to distil a por- 
tion of the fluid deposited during the condensation of oil gas, 
to set aside the product obtained before the temperature rises 
to 170°, to collect that which comes over by 180°, again 
separately that which comes over by 190°, and also the por- 
tion up to 200° or 210°. That before 170° will upon re- 
distillation yield portions to be added to those of 180° and 
190°; and the part obtained from 190° upwards will also, 
when redistilled, yield quantities boiling over at 180°, 190°, 
&c. Having then these three portions obtained at 180°, 190°, 
and 200°, let them be rectified one after the other, and the 
products between 175® and 195° received in three or four 
parts at successive temperatures. Then proceed with these 
as before described. 
It will sometimes happen, when the proportion of bi-car- 
buret of hydrogen is small in the liquid, that the rectifications 
must be many times repeated before the fluids at 185^ and 
190° will deposit crystals on cooling; that is to say, before 
suflicient of the permanently fluid part at low temperatures 
has been removed, to leave a solution so saturated as to 
crystallize at 0°. 
Bi-carburet of hydrogen appears in common circumstances 
as a colourless transparent liquid, having an odour resem- 
bling that of oil gas, and partaking also of that of al- 
monds. Its specific gravity is nearly 0.85 at 60°. When 
cooled to about 32° it crystallizes, becoming solid ; and the 
portions which are on the sides of the glass exhibit dendritical 
forms. By having tubes containing thin solid films of it in 
ice-cold water, and allowing the temperature to rise slowly, 
its fusing point was found to be very nearly 42° F. ; but when 
