OILY OXIDES, SAPONIFIABLE. 



It is a generally received opinion that sugar of milk is inca- 

 pable of fermenting, or of being decomposed into carbonic acid 

 and alcohol. But the well-known fact, that the Tartars and the 

 inhabitants of the Shetland Islands make an intoxicating liquor 

 by fermenting milk, is inconsistent with this opinion, and proves 

 that sugar of milk when properly treated may be made to fer- 

 ment as well as common and grape sugar. Doubtless, like com- 

 mon sugar, it is first converted into sugar of grapes before it 

 can be capable of fermenting or of being decomposed into alco- 

 hol and carbonic acid. 



CHAPTER III. 



OF OILY OXIDES, SAPONIFIABLE. 



THE terms fat, tallow, suet, lard, &c. are applied to a secre- 

 tion of an oily nature, usually solid in the hot-blooded, and 

 fluid in cold-blooded animals. This substance is deposited in 

 the cellular substance. The quantity formed depends in some 

 measure upon the food ; and when the food becomes deficient, 

 or the power of digestion imperfect, the fat disappears. It is 

 deposited in the cellular tissue of all animals, but the fat of only 

 a small number of species has hitherto been examined by che- 

 mists. Of these the following are the most important : 

 * 



1. HOG'S LARD. 



This is the fat of the Sus scrofa, or common hog. It is depo- 

 sited to a considerable thickness immediately under the skin 

 of the domestic animal. It is white, and has very little smell ; 

 but when we melt it in contact of boiling-water, the smell becomes 

 strong and disagreeable. It melts completely at 99, and then has 

 the appearance of a transparent and nearly colourless fixed oil. 

 A thermometer placed in it sinks gradually to 80. The lard 

 then begins to congeal, and the thermometer remains at 80 all 

 the time of congealing, which occupies several minutes. It is 

 clear from this that 80 is the melting point of hog's lard. 

 Its specific gravity at 102 is 0*9028 ; at 60 it is 0-9302. 



When hog's lard is left exposed to the air, it becomes gra- 

 dually yellow-coloured and rancid, acquires a strong smell, and 

 reddens vegetable blues. A volatile fatty acid is developed, th 



