URIC ACID AND CREATININE 211 



this stage. A little strong HC1 (1 c.c.) is next added to the contents of the 

 basin, and the whole is then heated over a burner until it just reaches the 

 boiling point. It is then set aside for the uric acid to crystallise out. 



If the mixture is artificially cooled all the uric acid will separate out in 

 two hours, otherwise it is best allowed to stand overnight or longer. 



The crystals are filtered off through a very small filter paper (4 cm. 

 diani.) ; the filtrate is received into a graduated cylinder so that the 

 amount of mother liquid may be noted (see below). The uric acid is next 

 washed with cold distilled water until free from chlorides. It is unnecessary 

 to transfer the whole to the filter ; the greater part may be washed by decanta- 

 tion. Such of the crystals as are upon the filter are now washed back into 

 the basin (best by the aid of hot water) and the whole quantity is dissolved 

 by heating to boiling with 1 c.c. of 10-per-cent. sodium carbonate solution 

 and as much distilled water as the basin will safely hold. 



The solution is transferred to a \ -litre Erlenmeyer flask, which should be 

 marked roughly at 100 c.c. The solution is made up to this mark with dis- 

 tilled water, and cooled to the temperature of the room. 



Twenty c.c. of strong sulphuric acid are added to the contents of the 

 flask, and the mixture shaken and titrated with the standard permanganate 

 solution. 



During the addition of the standard solution the liquid in the flask should 

 be kept in vigorous movement. It will be found that at first the disappear- 

 ance of the pink colour is so rapid that each drop as it is added is decolorised 

 before it has time to diffuse through the whole liquid. The first instan- 

 taneous appearance of a diffused flush throughout the solution indicates the 

 end point of the reaction. This colour rapidly disappears, but it will be found 

 that the effect of adding further quantities of permanganate after the end 

 point has been passed is quite different from the effect before the end point 

 was reached ; each drop is now able to diffuse throughout the fluid. 



For each c.c. of the solution necessary to produce the end point just 

 described 0*00375 gramme of uric acid is present. To the value so obtained 

 1 mgiii. must be added for each 15 c.c. of the mother liquor from which the 

 crystals separated. Thus the uric acid from 100 c.c. of a sample of urine 

 used up 18-5 c.c. of the 'standard permanganate solution. The mother liquor 

 filtered from crystals measured 25 c.c. 



18-5 x -00375 = -0694 gr. 



9^ 



001 x = -0017 



15 



Total = -0711 



The urine contained 71 mgms. uric acid per 100 c.c. 



3. Estimation of Creatinine. The following colorimetric method (Folin's) 

 is now generally employed for the estimation of creatinine; and with a 

 slight modification it may also be used for the estimation of creatine. It is 

 based on the red colour which Jaffe showed develops when an alkaline solu- 

 tion of picric acid is added to a solution of creatinine ; this is compared 

 with the colour of a standard solution of potassium bichromate, the tint of 

 the two fluids being almost identical. If creatine has to be estimated, this is 



