158 TESTING OF THE DIALVSIXG TUBES 



transfer the dialysates into the test-tubes by means 

 of one pipette. It is essential to have at one's dis- 

 posal for the actual tests as many different pipettes, 

 graduated to 10 c.c., as there are dialysates to be 

 handled. The test-tubes must also be absolutely 

 clean and dry, and they must be of exactly the same 

 width. Pouring the dialysates into the test-tubes is 

 not admissible, because the toluol may easily spoil the 

 reaction, chiefly by preventing satisfactory boiling. 



In detail one proceeds as follows : As before, the 

 pipette, closed at the top with the finger, is passed 

 through the toluol layer, and 10 c.c. of the dialysate 

 are withdrawn. The pipette is kept closed when 

 passing through the toluol layer, in order to prevent 

 any toluol from entering it. After transferring 

 10 c.c. of all the dialysates into the test-tubes, using 

 separate pipettes for each, we add to each test exactly 

 o'2 c.c. of an accurately prepared i per cent, solution 

 of ninhydrin. 



For accurate measurements a capillary pipette of 

 i c.c. is used. The ninhydrin solution is prepared 

 as follows : ninhydrin is usually sold in o'i-gr. 

 packets, and this quantity is shaken out of the tube 

 into a measuring flask marked to 10 c.c. The tube 

 is best emptied by tapping it against the inside of 

 the mouth of the measure, though it is not possible 

 by this means to transfer the whole of the o'i gr. of 

 ninhvdrin into the measure. The rest of the nin- 



