499 
In the experiments it is therefore especially necessary to exclude 
the dangerous air-nuclei, and, at the same time, to give the solutions 
sufficient opportunity to reach the equilibrium condition. 
The experiments of SroBBE and ScHöNBure were repeated with 
due regard to these considerations in the following manner. The 
solutions were prepared some time before the distillation and were 
kept during this time in the dark. At the same time the solutions 
were several times transferred to another flask. During this process 
the air nuclei were got rid of by transferring the solution first of 
all to a small flask which was filled to the brim, blowing away 
the air above it, and then pouring it into the new flask. Before use 
any nuclei still remaining in the air above the solution were 
removed by filling outside the laboratory a small measuring cylinder 
to the brim with the solution and blowing away the air over it. 
The solution was then poured from the cylinder through a glass 
funnel into a distillation flask (50 e.e. to 100 e.c.). The latter was 
closed by means of a cork through which passed a glass tube 
reaching to the middle of the bulb of the flask. A plug of cotton 
wool was inserted into the glass tube, while a larger plug was tied 
round the tube externally, fitting into the neck of the flask above 
the side-tube. Both the flask and the tube with the plugs were 
heated for several hours beforehand in a steam-heated air oven. In 
fitting them together care was taken that the fingers did not come 
into contact with any interior part. 
In order to exelude the possibility of accidental inoculation, a 
rapid current of air saturated with the solvent was drawn through 
ihe flask for about five minutes. The air was led in through the 
tube, so that any atmospherie nuclei present could be carried off 
through the side-tube. The cork was now raised a little, and, by 
means of a copper wire, which had been heated red-hot, the larger 
of the cotton wool plugs was pushed below the side-tube of the 
flask. The latter was then closed again by the cork. 
Since Srosppe and Scnönrsure observed that the melting of the 
68°- and the 58°-acid, which takes place in petroleum ether and in 
water at 50° and 40°—42° respectively, must be avoided, as this 
gives rise to the formation of 42°-acid, it was necessary to drive 
off the solvent at a temperature not exceeding 35°. At this tempera- 
ture they found no transformation of the two higher melting forms 
into the 42°-acid. 
When the concentration of the solutions was small, the distillation 
was generally effected in a partial vacuum, while with more 
concentrated solutions the solvent was evaporated by means of a 
