with too much toluol, or if the tube at the beginning of the test has not been immersed sufficiently deeply, then it may easily happen that, during the introduction of the pipette, some of the liquid passes from the outside into the dialysing tube. While, if one sucks strongly with the pipette at that moment, then the reverse may occur, and the contents of the tube may enter the pipette.
Ten cubic centimetres of the dialysate are taken, by means of a closed pipette passed through the toluol layer, and poured into a dry, wide, and absolutely clean test-tube. For each dialysate, as a matter of course, a separate, absolutely clean and dry pipette is used. One's work should never be arranged in such a manner that the pipette has to be hurriedly cleansed with alcohol, water, or ether after use, for the cleaning in this case may very easily be insufficient.
The danger of soiling the pipette with saliva is particularly great. (Compare p. 153.)
Then 0.2 c.c. of the 1 per cent. aqueous solution of ninhydrin are added to each test, together with a dry boiling rod (see p. 159), and one test after another is boiled absolutely evenly for a whole minute (see p. 160). After half an hour we ascertain which tests show a coloration and which do not, and only then do we compare our results with the original dialysates. If there be any tests which have evaporated more than the others, they are rejected, if they show a positive
