URIC ACID AND CREATININE 175 



more than 20-30 c.c. of water need be employed in this transference : if much 

 more has been used the liquid should be concentrated over the water bath at 

 this stage. A little strong HCl (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 crystalhse out. 



Titration of the uric acid. — If the mixture is artificially cooled all the 

 uric acid will separate out in two hours, otherwise it is best allowed to stand 

 over night or longer. 



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

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

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

 washed with cold distilled water until fi"ee firom 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 boUing with 1 c.c. of 10-per-cent. sodium carbonate solution 

 and as much distilled water as the basin wiU 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. 



The standard permanganate solution being ready in a burette, 20 c.c. of 

 strong sulphuric acid are added to the contents of the flask, and the mixture 

 shaken and titrated. 



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 foimd 

 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 gi-amme of uric acid is present. To the value so obtained 

 1 mgm. 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 the 

 crystals measured 25 c.c. 



18-5 X -00375 = -0694 gr. nearly 



•001 X ^^ = -0017 

 15 



Total = -0711 



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



3. Estimation of Creatinine. — The crystalline compound which creatinine 

 forms with zinc chloride is employed in estimating the quantity of creatinine 

 in urine ; 100 parts of the compound correspond to 62-42 of creatinine. 



Method. — Take 250 c.c. of urine. Add milk of hme and calcium chloride 



