430 



PBACTICAL PHYSIOLOGY 



for five minutes. Fill up the flask to the 500 c.c. mark, and mix well. By means 

 of a Dubosq or other suitable colorimeter determine the depth of liquid required 

 to give in daylight an intensity of colour exactly equal to that given by a depth 



of 8 mm. of a solu- 

 tion containing 24 '55 

 grm. pure potassium 

 bichromate per litre. 

 The readings of the 

 colorimeter, of which 

 several should be 

 taken, should be 

 completed within 

 twenty minutes of 

 the dilution, as the 

 reaction liquid fre- 

 quently fades. The 

 zero of both sides 

 of the colorimeter 

 should be tested, and 

 it is as well to test 

 the use of the colori- 

 meter by employing 

 the bichromate 

 solution on both sides 

 before determining 

 the creatinin. The 

 readings in the crea- 

 tinin determination 

 should not differ by 

 more than 0*3 mm. 

 If the average read- 

 ing is less than 5 

 mm. , the urine should 



be carefully diluted and another determination made; if above 13 mm., 20 c.c. 

 urine instead of 10 c.c. should be employed. 



The result of the determination is calculated from the formula : 



10x8-1 



FIG. 246. The Dubosq Colorimeter. 



Where x is the quantity of creatinin in milligrammes in the volume of urine 

 employed, and a is the colorimeter reading in millimetres. The amount of 

 creatinin is inversely proportional to the colorimeter reading. The formula 

 depends on the fact that, when 10 mg. of pure creatinin was employed for a 

 determination, the colorimeter reading, against 8 mm. of standard bichromate, 

 was 8'1 mm. 



Estimation of Creatin. Place in a flask, fitted with a cork and glass tube 

 to serve as condenser, 10 c.c. urine and 5 c.c. N. HC1. Heat the flask in a boiling 

 water bath for five hours. Cool to room temperature. Add sufficient caustic 

 soda to neutralise the acid added, 15 c.c. picric acid solution and 5 c.c. 10 per 

 cent, caustic soda. Allow to stand for five minutes. Wash the contents of the 

 flask into a 500 c.c. flask, make up to 500 c.c., and proceed as for creatinin. 



