37 8 PHYSIOLOGICAL CHEMISTRY. 



sible, however, by experimenting with known artificial mix- 

 tures, to determine the extent of this modification and so be 

 able to introduce a correction. For the present purpose the 

 disturbing action of the other urinary constituents on sodium 

 chloride is all that is called for. This has been done, but the 

 details of the investigation can not be given here. 



In a long series of experiments it was found that a mean 

 correction for the effect of sodium chloride may be made in this 

 way. The chlorine is accurately determined in the urine and 

 calculated as sodium chloride. From conductivity tables the 

 value of K for the calculated concentration is found and this 

 value is diminished by 3 per cent which is the average correc- 

 tion due to the presence of other substances, organic and inor- 

 ganic, in the urine. This corrected salt conductivity in turn 

 must be subtracted from the observed total conductivity to 

 find the fraction due to metabolic products. This correction 

 gives a result which is near the truth in ordinary normal urines 

 and which may be taken as furnishing a peculiar kind of meas- 

 ure of the total metabolism, that will be found to have a value 

 in certain calculations. 



THE FREEZING POINT OF URINE. CRYOSCOPY. 



In the thirteenth chapter the application of cryoscopic 

 methods to blood examinations was discussed, and the appa- 

 ratus used described. In urine investigations also freezing 

 point determinations have become important and a very con- 

 siderable literature has accumulated. The Beckmann appa- 

 ratus may be employed, as with the blood, but the Zikel modi- 

 fication has been found to give good results and is somewhat 

 simpler in manipulation. 



Conductivity and cryoscopic methods do not yield exactly 

 parallel results; the conductivity power of the urine depends 

 essentially on the number of inorganic molecules or ions pres- 

 ent, while the freezing point depression depends on the sum 

 of all the dissolved substances. Urea is therefore important 



