212 ESSENTIALS OF CHEMICAL PHYSIOLOQ-Y 



first transformed into creatinine by boiling with hydrochloric acid. The 

 apparatus and reagents necessaiy are : 



1. A colorimeter consisting of two tubes, the height of the column in 

 which can be read by graduations in tenths of a millimetre. 



2. A half normal solution of potassium bichromate (24'5 grammes per 

 litre). 



3. A saturated solution of picric acid. 



4. 10 per cent, caustic soda. 



To perform the analysis one tube of the colorimeter is filled with the 

 bichromate solution up to the height of 8 mm. Ten c.c. of urine are measured 

 into a half-litre flask, 15 c.c. of the picric acid solution and 5 c.c. of the 

 caustic soda solution added, and then water until the total volume of the 

 mixture is 500 c.c. This solution is poured into the second tube of the colori- 

 meter to such a height (which is read off) that, on looking down through it 

 the intensity of the colour is the same as that in the standard tube by its 

 side. The amount necessary for this corresponds exactly to 8-1 milligrammes 

 of creatinine. From this the total in the sample of urine can be easily 

 calculated. 



