518 APPENDIX* 



solution of carbonate of soda is added, the mixture soon becomes 

 yellow when treated with an excess of the solution of mercury, 

 but it remains white when the solution of mercury is insufficient 

 to precipitate all the urea. Very different methods may of course 

 be employed for the preparation of the test-fluid (of nitrate of 

 mercury) ; Liebig has, however, proposed a very simple method 

 for this purpose, which consists in treating nitrate of mercury, in 

 place of the bichloride, with phosphate of soda ; if, however, a 

 solution of common salt, of known concentration, be added to a 

 mixture of these salts before the precipitate of the phosphate 

 of mercury is rendered crystalline, the quantity of the oxide of 

 mercury may be very easily calculated from the volume of the 

 chloride of sodium necessary for its re-solution (for one equivalent 

 of chloride of sodium necessarily corresponds to one equivalent of 

 the phosphate of mercury). We may, however, at once obtain a 

 solution of chloride of sodium suited for the purposes of these 

 experiments, when we consider that a solution which is saturated 

 between the temperatures of and 100 constantly contains 

 27 of salt. 



The method of determining the amount of chlorine in the 

 urine is based upon the fact that, on the one hand, urea may be 

 precipitated by the nitrate but not by the bichloride of mercury, 

 and, on the other hand, that the nitrate becomes converted into 

 bichloride of mercury when brought in contact with chloride of 

 sodium. In order, therefore, to find the amount of chlorine in 

 the urine, a definite volume of it should be decomposed with the 

 solution of baryta ; the urine which is filtered from the precipitate 

 should then be treated with nitric acid until it is completely 

 neutralised, and the solution of the nitrate of mercury poured 

 upon it until the precipitate no longer dissolves on being stirred 

 (that is to say, as long as bichloride of mercury is formed). The 

 quantity of the bichloride of mercury, or of the chlorine, contained 

 in the urine may be calculated from the volume of the solution of 

 mercury which has been used. 



The amount of the secretion of urine exhibits greater fluctua- 

 tions than the secretion of any other organ. So many of the most 

 varied external and internal conditions here come into play, that 

 it would be impossible to estimate them perfectly, either for 

 special or general cases. Although we may form to ourselves a 

 tolerably correct idea of the more remote influences acting upon 

 the secretion of urine, and of their extent, we are still very 

 deficient in the knowledge of the more immediate conditions 



