DESTRUCTIVE DISTILLATION OF ANIMAL SUBSTANCES. 465 
spread in a thin layer on a glass plate, it is seen to be brown by transmitted light. 
Its specific gravity is about 0:970. Its smell is peculiarly disagreeable, and is mixed 
with that of ammonia, which is always present, though sometimes in so small 
quantity that its odour is disguised by that of the oil itself, and is only rendered 
apparent by distillation. A piece of fir-wood moistened with hydrochloric acid, 
and held over the mouth of a vessel containing it, rapidly acquires the dark red- 
dish-purple colour which is characteristic of the pyrrol of Runer. Acids agitated 
with the oil acquire a brown colour, especially on standing, and extract the bases 
contained in it; but if the quantity of the acid be large, and in a pretty concen- 
trated state, a nonbasic oil is also dissolved, which, on standing for some time, 
and more rapidly if heated, undergoes decomposition, and the fluid becomes filled 
with orange-yellow flocks of a resinous substance, which acquires a dark colour 
by exposure to the air ; this change is produced by the stronger vegetable as well 
as the mineral acids. Alkalies extract an acid oil, and a considerable quantity 
of hydrocyanic acid, which, on the addition of an acid to the alkaline solution, 
and distillation, can be distinguished in the product by its smell, as well as by 
_ Its reaction with the salts of iron. 
Previous to the seperation of the bases, the crude oil was again rectified in 
portions of about fifteen pounds each, in an iron retort,—an operation attended 
with some trouble, as the fluid is apt to froth up and boil over in the early part 
of the process, so that the retort must not be more than half full, and the heat 
requires to be applied in a very gradual manner. At first a watery fluid distils, 
containing in solution ammonia, and a small quantity of the most volatile bases. 
This is accompanied by an oil of a pale yellow colour, limpid and very volatile, 
which after a time comes over without water, and with an increased though by no 
means dark colour. The distillation proceeds in a perfectly steady and gradual 
manner, until about two-fifths of the oil have passed over, when a point is attained 
at which the temperature requires to be considerably raised, in order that the dis- 
tillation may continue uniformly, and the product becomes much thicker and 
more oily in its appearance. At this point the receiver was changed for the pur- 
pose of collecting the less volatile portion apart, and the distillation continued 
until the bottom of the retort reached a red heat. The latter portions of these 
products were obviously altered during the distillation, for a bulky porous char- 
coal remained in the retort ; the oil which passed over smelt strongly of ammonia, 
crystals of carbonate of ammonia made their appearance in the neck of the re- 
tort, and a certain quantity of water collected in the receiver. The oil also be- 
came gradually darker in colour, and more viscid in its consistence. By collect- 
ing in a succession of receivers, I had an opportunity of observing a great number 
of curious optical phenomena at different epochs of the distillation. The oils fre- 
| quently presented well-marked appearances of epipolic dispersion, and the very 

last portion exhibited a curious species of dichroism, its colour being dark reddish- 
