212 
Dr. Kidd's observations 
perfectly transparent, and amounted to rather more than a 
quarter of a pint : but there is ground for believing, from the 
results of subsequent distillations, that the proportion of the 
aqueous product is variable ; and that it is greater when the 
distillation is carried on slowly, than when it is carried on 
rapidly. 
After the above-mentioned products had passed over, a 
concrete substance as white as snow began to collect in dis- 
persed crystalline flocculi, in the upper part of the body and 
neck of the retort, so as in a short time almost wholly to 
obstruct the passage ; the oily fluid and the water continuing 
to pass over at the same time, but much more slowly than 
before. 
At the end of sixty hours the original quantity of the dark 
coloured liquid was reduced to about a quarter of a pint ; 
and what remained was much thickened in consistence : the 
heat was therefore increased : and now there began to pass 
over a darker coloured and thicker oil, which, as it advanced 
farther from the source of heat, congealed into a substance 
of the consistence of butter. The heat being still more in- 
creased, this oil became darker coloured and more dense ; and 
when at the last there remained in the retort not above one- 
eighth of the quantity originally poured into it, and the heat 
of the gas burner had been increased to the utmost, there 
arose a heavy yellow vapour, which was condensed in the 
neck of the retort in the form of a farina of a bright yellow 
colour. 
When it appeared that the heat no longer separated any 
thing from the black matter in the retort, which still however 
retained a degree of fluidity, the apparatus was suffered to 
