THE DIALYSATION PROCESS 149 



tube be very dense and allow little or no passage at 

 all of the peptones, we should naturally have in this 

 a considerable source of error. 



Numerous dialysing membranes are known, of 

 which very few have any real value for our purpose. 

 The dialysation process requires dialysing tubes which 

 can be used over and over again. The best are 

 those supplied by Schleicher and Schiill, of Diiren in 

 Rhineland. The tubes of this firm should in no case 

 be used without a thorough preliminary examination, 

 because tubes are nearly always met with which allow 

 albumen to pass through, while others are found 

 'through which peptones diffuse with difficulty, so 

 that careful testing of the tubes is indispensable. 13 

 Further, the tubes must be short ones. No. 57QA 

 is a tube specially prepared for our purpose. If 

 tubes be used, which project too much over the 

 surface of the surrounding fluid towards which 

 the dialysing process acts, this gives rise to a very 

 uneven evaporation of the dialysate. The latter 

 soaks into the tube, is carried upwards, and 

 evaporates. Indeed, as we shall see later, everything 

 depends upon the fact that, in comparative experi- 

 ments, the concentration of the dialvsates shall not 



Tested tubes are supplied by Schops, of Halle a/S., 

 but still it is advisable to test them, previous to use, as a 

 matter of security. 



