150 THE DIALYSAT1ON PROCESS 



be affected by unequal evaporation ; and every pre- 

 caution must be taken to avoid this source of error. 



The first duty to be undertaken in making use of 

 the dialysation process, is the testing of the tubes, 

 the so-called standardization of the dialysing tubes. 

 This standardization, as we have already emphasized, 

 implies the impermeability of the tubes towards 

 albumen, and a perfectly equal permeability for the 

 products of its decomposition. 



(a) Test for Impermeability by Albumen. A solu- 

 tion of albumen is prepared. The simplest way is 

 to take the white of a new-laid egg. 5 c.c. of per- 

 fectly fresh white of egg are diluted with distilled 

 water in a graduated tube to 100 c.c., and thoroughly 

 mixed by shaking. Of the white of egg, which must 

 be absolutely fresh, only the more fluid portion is 

 used, while all flaky matter or bits of skin in short, 

 all solid parts are rejected, as otherwise it is im- 

 possible to get a good mixture. Instead of the white 

 of an egg, blood serum may be employed. 



Now the tubes to be tested are prepared. They 

 are soaked in cold water for about half an hour. The 

 tubes are then placed in small Erlenmeyer flasks 

 (fig. 7) and 2*5 c.c. of the thoroughly mixed solu- 

 tion of white of egg in water are poured into them. 

 The solution is measured by means of a pipette. 

 While filling the tubes the pipette is placed far down 

 in them, and the greatest precautions must be taken 



