THE URINE. 417 



The calculation is simple. The 6.75 c. c. used contain 0.05 grm. 

 sugar, and the percentage of sugar in the dilute urine is therefore 



(6.75 : 0.05 = 100 : x) = ^ = 0.74. But as the urine was 



0. i O 



diluted with ten times its volume of water, the undiluted urine 



contained -=- = 7.4$. The general formula on using 10 c. c. 

 o. i o 



copper-sulphate solution is therefore r , in which n represents 



the number of times the urine has been diluted and k the number 

 of c. c. used for the titration of the diluted urine. 



The TITRATION ACCORDING TO KN APP depends on the fact that 

 mercuric cyanide is reduced into metallic mercury by grape-sugar. 

 The titration liquid should contain 10 grms. chemically pure dry 

 mercuric cyanide and 100 c. c. caustic-soda solution of a specific 

 gravity of 1.145 per litre. When the titration is performed as 

 described below (according to WORM MULLER and OTTO), 20 c. c. of 

 this solution should correspond to exactly 0.05 grm. grape-sugar. 



Also in this titration the quantity of sugar in the urine should 

 be between \% and 1%, and here also the extent of dilution necessary 

 must be determined by a preliminary test. To determine the end- 

 reaction as described below, the test for excess of mercury is made 

 with sulphuretted hydrogen. 



In performing the titration allow 20 c. c. of KNAPP'S solution to 

 flow into a flask and dilute with 80 c. c. water, or when you have 

 reason to think that the urine contains less than 0.5$ of sugar, then 

 only with 40-60 c. c. After this heat to boiling and allow the 

 dilute urine to flow gradually into the hot solution, at first 2 c. c., 

 then 1 c. c., then 0.5 c. c., then 0.2 c. c., and lastly 0.1 c. c. After 

 each addition let it boil J minute. When the end-reaction is 

 approaching, the liquid begins to clarify and the mercury separates 

 with the phosphates. The end-reaction is determined by taking a 

 drop of the upper layer of the liquid into a capillary tube and then 

 blowing it out on pure white filter-paper. The moist spot is first 

 held over a bottle containing fuming hydrochloric acid and then 

 over strong sulphuretted hydrogen. The presence of a minimum 

 quantity of mercury-salt in the liquid is shown by the spot becom- 

 ing yellowish, which is seen best when it is compared with a second 

 spot which has not been exposed to sulphuretted hydrogen. The 

 end-reaction is still clearer when a small part of the liquid is 

 filtered, acidified with acetic acid, and tested with sulphuretted 

 hydrogen (OTTO). The calculations are just as simple as for the 

 previous method. 



This titration, unlike the previous one, may be performed not 

 only in daylight, but also in artificial light. KNAPP'S method has 



