CONSTITUTION OF UREA, ETC. 4! 



decomposition of animal matter. It contains a residue of wood- 

 spirit and a residue of ammonia. 



Then we come to urea, which contains a residue of carbonic 

 acid and a residue of ammonia. In my first lecture I spoke of 

 urea as being the ammoniated form of carbonic acid as bearing 

 to carbonic acid the same relation that ammonia bears to water 

 whereas I now represent it as a compound of carbonic acid and 

 ammonia with elimination of water ; but a little consideration 

 will show that the two modes of regarding this and similar 

 bodies are substantially the same. The empirical formula for 

 carbonic acid by which I mean hydrated carbonic acid is 

 CH 2 3 , while that for urea is CH 4 N 2 O. But regarding the two 

 bodies as derivatives of the double atoms of water and ammonia 

 respectively, or as the hydrate and amide of carbonyl, these 

 formulae become (CO) // H 2 O 2 , corresponding to H 4 O 2 , and 

 (CO)"H 4 N 2 corresponding to H6N 2 respectively. Accordingly, 

 the representation of urea as a compound of carbonic acid and 

 ammonia with elimination of water, or as a variety of carbonic 

 acid in which certain elements of water are replaced by the cor- 

 responding elements of ammonia, is shown in these almost 

 identical equations : 



Carbonic acid z-Ammonia z-Water Urea 



CH a 3 + H 6 N 8 - H 4 a = 



(CO)H a O, + (H 3 )H 4 N a = (H a )H a O a + (CO)H 4 N, 



Glycocine, or sugar of gelatin, the next compound on the 

 list, contains, as I have already observed, a residue of ammonia and 

 a residue of gly colic or oxiacetic acid. Leucine, a body upon 

 which I shall offer some observations in a future lecture, is a homo- 

 logue of glycocine, and contains a residue of ammonia and a residue 

 of leucic acid. We now come to spermaceti, which contains a 

 residue of palmitic acid, an important member of our primary 

 series of fatty acids, united with the residue of a solid alcohol, the 

 cetylic, which bears to palmitic acid precisely the same relation that 

 common ethylic alcohol bears to acetic acid, so that spermaceti is 

 a true homologue of acetic ether, as shown in these equations : 



