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method of Folin is founded on the reaction of Jaffe, wliich consists 

 in adding picric acid and an excess of caustic soda to a solution of 

 creatinin, wliereat the liquid takes a brown colour, which cannot 

 be discerned from the colour of a solution of bichromate of potas- 

 sium. This reaction is employed in the following way : 5 cc. of 

 urine is mixed with 15 cc. picric acid 1,2 "/o ^"^1 5 cc. of caustic 

 soda 10 7o- After 5 minutes water is added to a volume of250cc. 

 This solution is compared by P'olin in the colorimeter of Duboscq 

 with a V, normal solution of bichromate of potassium of which a 

 column 8 mm. high shows exactly the same intensity of colour as 

 a column 8,1 mm. high of a solution of 10 mgr. creatinin Avitli 

 15 cc. picric acid solution and 5 cc. caustic soda diluted to 500 cc. 

 Instead of the colorimeter of Duboscq, Van Hoogeniiuyze and Yerploegh 

 used a little instrument, constructed after their indication, which 

 answered completely to their demands. Immediately after each deter- 

 mination each of them performed 5 readings of the height of the 

 solution of creatinin at which its colour had just the same intensity 

 as a column 8 mm. high of the solution of bichromate of potassium. 

 The several readings of which the average was taken, never differed 

 more than 0,2, only very seldom more than 0,1 mm. 



It proved meanwhile that the temperature has influence on the 

 reaction in that sense that the colour of the creatinin solution be- 

 comes deeper by increase of temperature. Therefore the water used 

 for the diluting was always kept at a temperature scarcely differing 

 from 15'' C. The relation found by Folin was affirmed. A solution 

 of 10 mgr. of pure creatinin in 500 cc. treated in the indicated 

 way produced as the average of 10 readings 8.14 m.m. (max : 8.2, 

 min. 8.1) out of which a quantity of 9.951 instead of 10 mgr. 

 would be deduced. 



The results become less exact when the concentration of creatinin 

 is much larger or smaller than 10 mgr. in 500 cc. Therefore the 

 determination was repeated when the readings became higher than 10.5 

 or lower than 5, with 10 cc. urine, in the first case diluted to 250 

 in the second to 1000 cc The method of Folin had great advantages 

 over the method of Neubauer used till now, in which the creatinin 

 is precipitated out of an alcoholic extract of the urine by means of 

 chloride of zinc and after that weighed. Kot only that the method of 

 Folin takes much smaller quantities of urine, so that it renders it easy 

 to discern by the examination of different portions of urine the oscilla- 

 tions in the secretion in the course of the day, but it is also more 

 reliable. With the method of Neubauer there is always some danger 

 that under the influence of the alkaline reaction arising from the addi- 



