734 PHYSIOLOGICAL CHEMISTRY. 



c.c. of urine used. Suppose 30 c.c. of urine, diluted with 9 parts of 

 water, or 3 c.c. of pure urine, have been required to decompose the 10 

 c.c. of Fehling's solution, then 3 c c. of urine contain of grape-sugar 

 0.05 gramme, or 100 c.c. of urine 1.666 grammes, according to the 

 proportion : 



3 : 0.05 : : 100 : x 



1 = 1.666. 



If the urine contains but very little sugar, it may be used directly 

 without diluting it, or instead of diluting it with 9 parts of water, it 

 may be diluted with 4 volumes or with an equal volume of water. 



In using Fehling's solution for the volumetric estimation of lactose, 

 it should be remembered that 1 c.c. of solution is decomposed by 

 0.0067 gramme of lactose. 



Modified Fehling method (Rudisch and Celler). The only change is 

 in diluting the 10 c.c. of Fehling solution with 40 c.c. of 50 per 

 cent, potassium stilphocyanate instead of with 40 c.c. of water. The 

 end-reaction here is the same, i. e., the disappearance of the blue. As 

 there is no precipitate to obscure the end-point, the estimation is 

 readily made and the method is an improvement over the original 

 procedure. As the same amount of Fehling's solution is used, the 

 calculation is carried out in the same way. 



Harvey G. Beck has devised the following method : 



The apparatus used consists of a suitable beaker ; four centrifugal tubes 

 graduated at 2 c.c. ; a pipette of 2 c.c. capacity, graduated into twentieths c.c., 

 and a wire tube-holder to support the tubes when placed in the beaker. A 

 centrifuge will greatly facilitate the work. 



The procedure is as follows : The beaker, one-third full of water, is placed 

 over a.Bunseu flame, and the four centrifugal tubes, after being filled to the 

 graduation mark (2 c.c.) with standard Fehling's solution, are placed in the 

 tube-holder and suspended in the beaker. The tubes are numbered respectively 

 1, 2, 3, and 4, according to their position in the tube-holder. The urine is added 

 from the pipette in quantities of twentieths c.c., as follows: fa to No. 1, -fa to 

 No. 2, fa to No. 3, and -fa to No. 4. The tubes, after being thoroughly shaken, 

 are suspended in boiling water for at least three minutes, when they are removed 

 and either set aside in the tube-stand until the cupric oxide is precipitated, or 

 centrifugalized in order to hasten precipitation. If all the tubes still show a 

 blue color, the urine is increased to ^, -fa, $%, and fa respectively, by adding 

 fa e.c. to each tube, and the foregoing steps are repeated. This process is con- 

 tinued until one, or more, of the tubes is completely decolorized. The first tube 

 in the series in which the blue color has entirely disappeared is noted; the 

 number of twentieths c.c. required to reduce it, divided into twenty, gives the 

 percentage of sugar present. 



Estimation by fermentation can be readily done, using specially 

 graduated tubes, which can be read directly in percentages of dextrose. 



