THE 



formerly employed a solution which contained a mixture of Copper 

 sulphate, Rochelle salt, and sodium or potassium hydrate (FEH- 

 LING'S solution) ; but as such a solution readily changes, we now 

 prepare a copper-sulphate solution and an alkaline Kochelle-salt 

 solution separately, and mix equal volumes of the two solutions 

 before using. 



The concentration of the copper-sulphate solution is such that 

 10 c. c. of this solution is reduced by 0.05 grm. grape-sugar. The 

 copper-sulphate solution contains 34.65 grms. pure, crystallized, non- 

 efflorescent copper sulphate in 1 litre. The sulphate is crystallized 

 from a hot saturated solution by cooling and stirring; and the 

 crystals are separated from the mother-liquor and pressed between 

 blotting-paper until dry. The Rochelle-salt solution is prepared 

 by dissolving 173 grms. of the salt in 350 c. c. water, adding 600 

 c. c. of a caustic-soda solution of a specific gravity of 1.12, and dilut- 

 ing with water to 1 litre. According to WORM MULLER, these 

 three liquids Rochelle-salt solution, caustic soda, and water 

 should be separately boiled before mixing together. For each 

 titration mix in a small flask or porcelain dish exactly 10 c. c. of 

 the copper-sulphate solution and 10 c. c. of the alkaline Rochelle- 

 salt solution and add 30 c. c. water. 



The urine free from albumin is diluted before the titration 

 with water so that 10 c. c. of the copper solution requires between 

 5 and 10 c. c. of the diluted urine, which corresponds to between 

 1 and \% sugar. A urine of a specific gravity of 1.030 may be 

 diluted five times; one more concentrated, ten times. The urine 

 so diluted is poured into a burette and allowed to flow into the 

 boiling copper-sulphate and Rochelle-salt solution until the copper 

 oxide is completely reduced. This has taken place when, after 

 boiling, the blue color of the solution disappears. It is very dif- 

 ficult and requires some practice to exactly determine this point, 

 especially when the copper suboxide settles with difficulty. To 

 determine whether the color has disappeared, allow the copper 

 suboxide to settle a little below the meniscus formed by the surface 

 of the liquid. If this layer is not blue, the operation is repeated, 

 adding 0.1 c. c. less of urine; and if, after the copper suboxide has 

 settled, the liquid has a blue color, the titration may be considered 

 as completed. Because of the difficulty in obtaining this point 

 exactly another end-reaction has been suggested. This consists in 

 filtering immediately after boiling a small portion of the treated 

 urine through a small filter into a test-tube which contains a little 

 acetic acid and a few drops of potassium-ferrocyanide solution and 

 water. The smallest quantity of copper is shown by a red colora- 

 tion. If the operation is quickly conducted so that no oxidation 

 of the suboxide into oxide takes place, this end-reaction is of value 

 for urines which are rich in sugar and poor in urea and which 



