CH. XIII.] MICRO-KJELDAHL. 329 



Remove the wooden blocks F, and then remove the flame. Remove 

 the rubber stopper from the upper end of the condenser and wash 

 the latter down into E with a jet of distilled water. Wash down 

 the exterior of D also, add a few drops of methyl red and titrate 

 with the CO 2 - free soda, as described on page 323. The soda can be 

 between 0-05 and o-i N. 



Calculation, see p. 323. 



397. Micro-Kjeldahl (Cole's method). Into a clean, dry, 

 boiling tube measure 0-5 or I cc. of the urine, using an Ostwald 

 pipette (fig. 48). Add 2 cc. of pure concentrated sulphuric acid and 

 2 drops of saturated copper sulphate. Mix and boil over a free 

 flame, shaking vigorously to prevent spurting, until dense white 

 fumes appear in the tube. A test-tube holder should be improvised 

 by the use of a piece of folded paper. Add i gram, of pure potassium 

 sulphate and heat again. Clamp the tube over a micro-burner, 

 having a flame about J inch in height, just touching the bottom of 

 the tube, and insert a Folin's fume-absorber (fig. 51) into the mouth 

 of the tube. Continue the gentle boiling for at least 5 minutes after 

 the solution has lost all trace of its dark colour and has turned light 

 blue. Allow to cool, add 10 cc. of distilled water, transfer the 

 solution to the tube B shewn in fig. 34, p. 261, and proceed 

 exactly as described in the last paragraph of Ex. 311. 



B. The Estimation of Ammonia. 



The ammonia of urine normally exists as ammonium salts of weak acids . 

 In cases of cystitis, however, the urine is nearly always alkaline, owing to the 

 conversion of some of the urea to ammonium carbonate by various micro- 

 organisms. This change may occur after the urine has been passed owing 

 to bacterial contamination from the air, etc. For this reason it is essential 

 that a little toluol should be added to the vessel in which the urine of the 

 24 hours is being collected, that it should be kept in a cool place and that the 

 estimations should be made as soon as possible. 



A great many methods have been proposed for the estimation of ammonia 

 in urine. Folin has introduced 'them at a rate which is almost alarming. 

 Indeed, one might be led to imagine that such a master of technique distrusts 

 his own methods so much that he is forced to strive for a better one. Nearly 

 all his later methods are colorimetric, a most excellent modification of Nessler's 

 solution having been elaborated. But the author's experience with large 

 classes is that the majority of workers prefer to use a titration method if 

 possible. Mainly for that reason, the only three methods described here are 

 Folin's original macro-method, Van Slyke's modification of it, and the formol 

 method. The latter, however, gives the sum of ammonia and the amino-acids, 



