8 Dr. Marcet on a Colloid Acid of Urine. [1864. 



nate of baryta, carbonic acid is evolved, the fluid becomes neutral, or very 

 sligbtly alkaline, and is found to contain baryta. If the insoluble lead-salt 

 of the acid be decomposed with sulphuric acid, and the filtrate from the sul- 

 phate of lead boiled with carbonate of baryta, the fluid becomes more deci- 

 dedly alkaline. The analysis and composition of this baryta-salt has been 

 given above ; the solution in a syrupy condition deposits no crystals. The 

 concentrated solution of the baryta-compound behaves as follows with 

 reagents. 



Basic acetate of lead : A bulky precipitate soluble in an excess ; the 

 precipitate reappears on addition of dilute nitric acid ; the further addi- 

 tion of nitric acid redissolves it. 



Neutral acetate of lead : A slight precipitate. 



Nitrate of silver : A slight precipitate readily soluble in nitric acid. 



"When the baryta-salt is boiled with carbonate of silver, but a small pro- 

 portion of the metallic carbonate is decomposed even after long-continued 

 boiling. 



Acid nitrate of mercury : A white precipitate becoming darker after a 

 short time. 



Tannic acid : A slight precipitate. 



It should be understood that the more concentrated the solution, the 

 more abundant are the precipitates. 



The Lime-Salt. The lime-salt exhibits the same characteristic reactions 

 as the baryta-salt ; it is formed by boiling the free acid with precipitated 

 carbonate of lime. The fluid remained acid after it had been boiled with 

 pounded marble, although some lime was dissolved ; concentrated to a cer- 

 tain point, the solution becomes thick and syrupy, but deposits no crys- 

 tals ; ammonia and oxalate of ammonia do not appear to precipitate com- 

 pletely the lime from the solution, but the precipitation is perfect by means 

 of sulphuric acid and alcohol. 



The Potash- and Soda-salts, We may infer from the earthy salts that 

 the potash- and soda-compounds of the colloid acid of urine have a slightly 

 alkaline reaction. There is no difficulty in neutralizing a given volume of 

 the colloid acid with a potash solution, but it is questionable whether a 

 definite chemical compound is thus obtained. 



Physiological Relations of the Colloid Acid of Urine. 



I have invariably found the colloid acid present in the urine, but its 

 mode of extraction described above is calculated to give us but a verv 

 rough insight into the quantity naturally contained in the secretion. After 

 decomposing the lead-precipitate 'by sulphuretted hydrogen, a process 

 which it must be remembered is a slow one, a given proportion of the fluid 

 may be evaporated to dryness, the residue dried at between 101 and 110 

 Cent., and its weight ascertained ; the result will be obtained somewhat 

 more accurately by determining the ashes of the residue, and subtracting 

 this weight from that of the residue. I have extracted from 8 litres of 



