316 



Dr. Marcet on a Colloid Acid. 



[June 16, 



compound with neutral acetate of lead, acetic acid was given off, a confir- 

 matory proof of the insoluble lead compound being an acid salt ; in this 

 case one equivalent of the colloid acid combines with one equivalent of 

 oxide of lead of the neutral acetate, two equivalents of the neutral lead-salt 

 of the colloid acid being thus formed, 



PbO, 2 (Acid) + PbO, C, H3 03= 2 (PbO, Acid) + C, H3 O3. 



This shows that it is not possible to estimate with accuracy the amount 

 of the acid in urine by means of basic acetate of lead. 



"When the acid is boiled with an excess of hydrated oxide of lead, 

 an insoluble compound is formed ; if the acid be in excess, a compound 

 soluble in hot water, but precipitating on cooling, is obtained : I have not 

 yet determined the composition of these two lead-salts. 



Baryta- and Lime-Salts, — These salts are easily prepared from the car- 

 bonates. They contain one equivalent of the acid, are soluble in water, 

 and yield precipitates with basic acetate of lead, nitrate of silver, and pro- 

 tonitrate of mercury and tannic acid ; the more concentrated the solution, 

 the more abundant the precipitates. A very slight precipitate occurs by 

 adding neutral acetate of lead to salts of the acid ; other reagents fail to 

 yield precipitates. 



The acid dissolves silver from the carbonate, but I could not neutralize 

 it perfectly by such means. The lime-salt of the acid cannot be entirely 

 decomposed by boiling it with carbonate of silver. 



When the acid is boiled with black oxide of copper, copper is readily 

 dissolved. 



Physiological relations of the Colloid Acid of TJrine. 



I endeavoured to determine approximately the quantity of the colloid in 

 a given bulk of the urinary secretion, and extracted from 8 litres 4*46 

 grammes of this substance, which, however, must fall short considerably 

 of the real amount of the acid present. 



It may be considered as existing in all probability in the blood, where 

 there is little doubt that it acts an important part in the phenomena of the 

 secretion of gastric juice, by displacing the hydrochloric acid from chloride 

 of sodium, combining with the sodium ; the soda-salt would remain in the 

 blood, being a colloid compound, while the free hydrochloric acid would 

 find its way into the stomach. xAn experiment I performed in connexion 

 with this subject bears out the present view. 



The formation of the colloid acid appears to result from some trans- 

 formation of the colloid non-nitrogenous constituent of the liver known as 

 the glucogenic substance. When better acquainted with the chemical 

 composition and physiological relations of the colloid acid of urine, I shall 

 be able to give it an appropriate name. 



