URINE. 103 



QUANTITATIVE DETERMINATIONS. 



PHYSICAL PROPERTIES. 



Determinations of certain physical properties of the 

 urine have come into prominence of late as a means for 

 furnishing additional data concerning the general state 

 of equilibrium which obtains in the fluid. The urine, being 

 in fact merely a somewhat dilute solution of organic and 

 inorganic salts, must possess the same properties and respond 

 to the same physical laws which govern such solutions. The 

 most important property whose determination is attempted 

 is that of the depression of the freezing-point below that of 

 the solvent, water. 



The law states that the presence bf substances dissolved 

 in a solvent causes the freezing-point of the solution to be 

 lower than that of the solvent, and that the amount of the 

 depression is in direct proportion to the number of molecules 

 or (when dissociation has taken place) ions in the solution. 



The depression of the freezing-point, which is represented 

 by the Greek letter J, is therefore dependent upon the 

 molecular concentration. 



The only substances which are present in the urine in a 

 quantity sufficient to exert any influence on J are the urea 

 and sodium chloride and possibly the phosphates and sul- 

 phates, although the effect of the latter two, even if it did lie 

 outside of the limit of experimental error, could not suffice 

 to cause differences which would influence deductions. The 

 other factors which affect the J are those which cause varia- 

 tions in the specific gravity of the urine, and it is stated that 

 ..a relationship exists between the two which only varies 

 -within very small limits. A priori, this seems impossible 



