Dr. Marcct on a Colloid Acid of Urine. 



[1864. 



substance is very 'hygroscopic, and dissolves readily in water (with the ex- 

 ception of some few dark flakes) after exposure for some time at 120 Cent. 

 Alcohol, sp. gr. 827, gives it a dull, opaque appearance, and slightly dis- 

 solves it. The dry acid is insoluble in ether, and its solution in diluted 

 alcohol is rendered turbid by ether. When burnt it chars, emitting a 

 pungent smell ; the ignition is attended with but a very faint flame, show- 

 ing that very little hydrogen enters into its composition ; nothing but a 

 trace of fixed inorganic residue remains after complete incineration of the 

 acid. The colloid acid was found to have no action on polarized light ; it 

 failed to precipitate egg-albumen, but precipitated casein in milk ; the pre- 

 cipitate was not redissolved in an excess of the acid, as in the case of 

 acetic acid ; although strictly a colloid, it passes through the diaphragm of 

 a dialyzer, but the phenomenon is not near so rapid as in the case of crys- 

 talloids. In an alkaline fluid, however, the acid (under the form of a 

 compound) does not find its way so readily through the dialyzer, and its 

 passage is thereby checked in a considerable degree. 



The qualitative composition of the colloid acid of urine was obtained by 

 subjecting to analysis its insoluble lead-compound. I found the organic 

 substance to consist only of carbon, hydrogen, and oxygen. I have not 

 yet determined the ultimate quantitative composition of the acid, but 

 have succeeded in showing that it possesses an atomic weight, or com- 

 bining proportion, thereby proving the acid to be a definite substance ; 

 the atomic weight of the acid was determined by the analysis of its inso- 

 luble lead-salt and of its baryta-salt. In order to analyze the insoluble 

 lead-salt, a weighed quantity of the compound, dried at 120 Cent., was 

 dissolved in acetic acid, and precipitated by means of sulphuric acid, with 

 the addition of alcohol ; the sulphate of lead was collected in a filter, the 

 filter burnt, and the inorganic residue treated with sulphuric acid ; the 

 sulphate of lead was finally weighed. 



TABLE showing the results obtained from the analysis of the insoluble 

 lead-salt of the Colloid Acid of Urine. 



100-0 



