462 Prof. Liebig on iJie Constitution of 



acid reaction. When employing sulphuric acid and hydro- 

 chloric acid the distillate was acid, but the acid reaction pro- 

 ceeded from hydrochloric acid. 



I have, in the preceding experiments, several times alluded 

 to a nitrogenous resin-like substance, which is present in all 

 the fluids obtained in the examination of putrid urine. This 

 substance is a product of the putrefaction of the urine, and is 

 of an acid nature. If the residue remaining upon the evapo- 

 ration of putritl urine is treated with alcohol, and the result- 

 ing solution boiled with addition of hydrate of lime, until am- 

 monia ceases to be given off, then evaporated to dryness, and 

 the residue treated with cold alcohol, there remains a mass of 

 a light brown colour, which, at a high temperature, may be 

 kneaded like resin, and drawn out into long threads, and 

 which, upon combustion, emits a strong smell of urine, and 

 leaves a quantity of carbonate of lime as ashes. 



If putrid urine is evaporated and sulphuric acid added, after 

 the lapse of some time, an oily, black-coloured substance se- 

 parates, which, being washed with water, assumes the appear- 

 ance of pitch. It is soluble in alcohol and in alkalies. Upon 

 distilling putrid urine with mineral acids this substance is ob- 

 tained in the residue to a considerable amount, although al- 

 tered in many of its properties. A portion of it, produced in 

 this manner, has, — apparently from the action of the acids at 

 a high temperature, — completely lost its solubility in alcohol, 

 whilst its solubility in alkalies remains unimpaired. From 

 this alkaline solution it may again be precipitated in black 

 flakes by acids. Proust has described these substances mi- 

 nutely, but as they cannot be procured from fresh urine, they 

 are, as products of the putrefaction of urine, of no interest in 

 the present investigation. 



Just as benzoic acid and a nitrogenous substance are pro- 

 ducts of the putrefaction of hippuric acid in urine, I consider 

 acetic acid and the above-mentioned nitrogenous resinous sub- 

 stance to stand in a definite relation to each other; that is, I 

 consider them to be products of the decomposition of a sub- 

 stance containing the elements of both ; and this substance 

 seems to be no other than the colouring matter of the urine. 

 Not the slightest trace of alcohol has ever been detected in urine 

 excreted after the use of spirituous liquors. It is evident, 

 therefore, that the acetic acid present in putrid urine cannot 

 owe its origin to the use of spirituous liquors. If sugar, or 

 sugar of milk, be added to fresh urine, and the urine is then 

 left to putrefy, the sugar or milk-sugar are found unaltered, 

 even after the lapse of three months. It is evident, therefore, 



