1 8 ANIMAL CHEMISTRY LECTURE I. 



whereas if we replace them by amidogen we get urea, as shown 

 in the second line of the table. Physiologists regard urea as 

 a complex organic body altogether sui generis. The chemist 

 regards it merely as the ammoniated form of one of the sim- 

 plest mineral acids; for the relation of phosgene and carbonic 

 acid to urea is identical with that of hydrochloric acid and 

 water to ammonia, and with that of chloride of potassium and 

 caustic potash to potassamide. Proceeding a little further, if in 

 cyanuric chloride C 3 N 3 C1 3 , we replace the three atoms of chlorine 

 by three atoms of peroxide of hydrogen, we get cyanuric or pyro- 

 uric acid; whereas if we replace them by amidogen, we get 

 melamine, a product of the action of heat upon urea. Passing 

 qn to chloracetic acid C 2 H 3 C10 2 a derivative of common acetic 

 acid C 2 H 4 2 , by the substitution of an atom of chlorine for hydro- 

 gen if in this body we replace the chlorine by peroxide of 

 hydrogen, we obtain glycolic acid ; whereas if we replace it by 

 amidogen, we obtain glycocine, or sugar of gelatin, glycocine 

 being only an ammoniated form of the glycolic and chlor- 

 acetic acids. 



The next formula, C 2 H 5 C1S0 3 , represents chlorethyl-sulphur- 

 ous acid, and if in this body we replace the atom of chlorine by 

 an atom of peroxide of hydrogen, we obtain isethionic acid; 

 whilst if we replace it by amidogen, we obtain a compound of 

 which I have already spoken, namely, ta urine, taurine, isethi- 

 onic acid, and chlorethyl-sulphurous acid being respectively the 

 amidated, hydrated, and chlorinated forms of one and the same 

 body, being, in fact, ethyl-sulphurous varieties of hydrochloric 

 acid, water, and ammonia. 



(17.) You perceive that this establishment between most com- 

 plicated and diverse bodies of relations similar to those subsisting 

 between hydrochloric acid, water, and ammonia between chlo- 

 ride of potassium, caustic potash, and potassamide furnishes us 

 with a key to the composition and metamorphoses of a whole 

 host of organic compounds ; but the generalisation is capable of 

 being pushed much farther. In bodies with two atoms of 

 chlorine, we may replace either one or both of them by eurhyzen, 



