196 MANURE. 



undergo no change when dissolved in pure water, but if they 

 are mixed with the other ingredients of the urine, decompo- 

 sition rapidly ensues, and they are resolved almost entirely 

 into carbonate of ammonia. Alkalies and alkaline earths 

 induce similar changes on urea. The practical value of this 

 fact will be easily understood. 



241. Pure urea has no distinct alkaline properties. It 

 unites with aqua fortis, or nitric acid, and forms a sparingly 

 soluble salt, composed of about equal parts of each of its 

 ingredients. 



242. Urea is composed, according to Dr. Prout, of car- 

 bon 19.99, oxygen 26.66, hydrogen QM, nitrogen, 46.66. 

 These elements are so beautifully balanced, that they afford 

 only carbonic acid and ammonia ; though the chemistry of 

 every reader may not understand how these elements pro- 

 duce cyanic acid and ammonia. The salt cyanate of ammo- 

 nia, has actually been formed by modern chemistry,^ which 

 has thus succeeded in forming a true organic product, or 

 product of living action, or rather of chemical action guided 

 by living principle. In all animal evacuations containing 

 urea, that may be considered as so much carbonate of 

 ammonia of the shops. Hence it is the urea in urine which 

 gives that liquid so great a value. Urine is richer in ammo- 

 nia than flesh or blood. 



243. The peculiar animal acid which has been mentioned 

 as forming so essential a part in these liquid excretions, is 

 called uric acid. It is not, like urea, changed by exposure 

 into ammonia. It contains a large portion of nitrogen, 

 which, under the influence of growing plants, is let loose, and 

 may then form ammonia. Its composition is as follows : 

 carbon 36.11, hydrogen, 2.34, oxygen 28.19, nitrogen 33.36. 

 - The peculiar principles of the liquid evacuations having 

 been explained, their constitution may be now stated. They 



