Destructive Distillation of Animal Substances. 177 



the acid be large, and in a pretty concentrated state, a non- 

 basic 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 con- 

 siderable 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 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 ac- 

 companied 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 distilla- 

 tion 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 distillation may continue uniformly, 

 and the product becomes much thicker and more oily in its 

 appearance. At this point the receiver was changed for the 

 purpose 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 obvi- 

 ously 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 retort, and a certain quan- 

 tity of water collected in the receiver. The oil also became 

 gradually darker in colour, and more viscid in its consistence. 

 By collecting in a succession of receivers, I had an opportu- 

 nity of observing a great number of curious optical phaenomena 

 at different epochs of the distillation. The oils frequently 

 presented well-marked appearances of epipolic dispersion, and 

 the very last portion exhibited a curious species of dichroism, 

 its colour being dark reddish-brown by transmitted, and green, 

 with the effect of opacity, by reflected light. All these ap- 

 pearances, however, were very evanescent, and are only seen 

 in the newly-distilled oil, for after a few days it becomes very 

 dark-coloured, and they are then no longer visible. 



