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 fii'-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 Runge. 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 Avell as by 

 its reaction with the salts of iron. 



Previous to the separation 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 temperatui'e 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 difierent 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- 



