92 ANIMAL CHEMISTRY LECTURE IV. 



Thus, among 2 -carbon products of the animal and vegetable 

 kingdom, that have been obtained by strictly mineral processes, 

 may be mentioned alcohol, taurine, acetic acid, glycocine, and 

 last, though not least important, oxalic acid; which results 

 from the oxidation of alcohol, acetic acid, and glycolic acid, &c., 

 and is producible synthetically from the mono-carbon formic and 

 carbonic acids. 



(96.) By means of the general processes to which I directed 

 your attention some time back, as well as by certain special 

 processes, it is easy to pass from the 2-carbon to the 3 -carbon 

 group, upon which, however, we must rest satisfied with be- 

 stowing a very cursory glance. It comprises among its members 

 glycerin C 3 H8O 3 , the basic principle of the true fats, whether 

 of vegetable or animal origin. Also lactic acid C 3 H6O 3 , an 

 important constituent of the juice of flesh, and a product of that 

 fermentation of grape-sugar and milk-sugar which is set up by 

 putrefying curd. We have also the chief constituents of essential 

 oil of garlic, or allyl-sulphide (C 3 H 5 ) 2 S, and of essential oil of 

 mustard, or allyl-sulphocyanate (0 3 H 5 )H.CNS, to be included in 

 the list of artificially produced members of the propionic family. 



(97.) Passing on to the 4-carbon group, we have first butyric 

 acid C 4 H8O 2 , a product of the destructive metamorphosis of 

 sugar, mannite, &c. Combined with alcohol it forms butyric 

 ether or essential oil of pine-apple, while combined with glycerin 

 it forms that constituent of ordinary butter which is known as 

 butyrin. Succinic acid C 4 H60 4 , is readily procurable from 

 butyric acid, and bears to it the same relation that oxalic bears 

 to acetic acid. It is probably the most frequent artificial product 

 of the oxidation of fatty matters, and has also been met with 

 naturally in the cystic fluids of hydatids, hydrocele, &c. From suc- 

 cinic acid it is easy to procure in succession the well-known vege- 

 table products, malic acid C 4 H6O 5 , and tartaric acid C 4 H6O6, 

 which, again, are reconvertible into succinic acid. The malic and 

 succinic acids, in particular, are very intimately associated with, 

 and readily convertible into, one another. Thus, asparagine 

 C 4 H8N 2 O 3 , the crystalline principle of asparagus and other 



