444 URINE. 



of a definite quantity of dilute sulphuric acid, which must sub- 

 sequently be accounted for in the analysis. 



We have already spoken, in the first volume, under their 

 respective heads, of the various methods adapted for the quantita- 

 tive determination of urea., uric acid., hippuric acid, sugar, albumen, 

 oxalate of lime, &c. Nor have we much to add in reference to the 

 quantitative determination of the mineral constituents of the urine 

 beyond what we have already stated of analyses of the ash in vol. i., 

 pp. 405-412. In case we do not wish to adopt Rose's method of de- 

 termining the ash, the process of carbonizing and incinerating the 

 residue of the urine may be considerably facilitated by adding to the 

 urine, before its evaporation, a quantity of nitric acid nearly equiva- 

 lent to its urea ; by this means nitrate of urea is formed, which 

 becomes decomposed on evaporation into carbonic acid and nitrate 

 of ammonia, and escapes, during further concentration, in the 

 form of water and nitrous oxide. Much time is gained by this method, 

 for the substance which constitutes the larger portion of the urinary 

 residue, and which yields a very large quantity of carbon on ex- 

 posure to a red heat, is in this manner almost entirely eliminated. It 

 might be feared that a portion of the alkaline chlorides would thus 

 be decomposed either by the nitric acid or the nitrous oxide ; but 

 from the direct experiments which I have made with this and with 

 the ordinary method, I find that there is no loss of chlorine unless 

 we add so much nitric acid that slight explosions occur on ex- 

 posing the solid residue to a red heat. But it is not possible, even 

 by this method, to consume the urinary residue so entirely as only 

 to leave a white ash, if we keep in view that we are attempting a 

 quantitative analysis, and have regard to the vapours of phosphorus 

 and chlorine which escape on intense heating. On account of 

 the presence of soluble and fusible salts, the carbonaceous residue 

 of the urine can scarcely ever be perfectly incinerated, for the 

 particles of carbon become invested by means of the fusible salt 

 with a crust, which protects them from the action of oxygen. As 

 this is the case even with very small quantities of the urinary resi- 

 due, I regard the following method as the best adapted for quan- 

 titatively determining the mineral constituents of the urine : the car- 

 bonaceous ash must be weighed with the caution necessary in the 

 case of hygroscopical bodies, and after being washed with water, 

 must be filtered; and the residue on the filter, whose weight in the 

 dry state has been previously ascertained, must be again weighed. 

 The difference of weights gives the amount of the mineral sub- 



