156 TESTING OF THE DIALYSING TUBES 



turbid owing to the deposition of copper hydroxide, 

 and the quite colourless liquid below. The slightest 

 trace of a pinkish-violet colour is a proof that the 

 tube from which the dialysate was procured is un- 

 suitable. Often the presence of albumen is shown by 

 the fact that the precipitated copper oxide dissolves 

 after a time in about half an hour and a clear violet 

 layer appears which gradually diffuses into the other 

 liquid. With this test it is better to be over-cautious, 

 and the tubes should be rejected each time the biuret 

 reaction gfives doubtful results. 



o 



(b) Testing of the Dial y sing Tubes for equal Per- 

 meability to Decomposites of Albumen.- -Tubes, 

 which do not allow the passage of albumen, 

 must first of all be thoroughly cleansed. Their con- 



O J 



tents are poured out, and they are then placed on a 

 sieve and rinsed for about half an hour in clean 

 running water. 



For the sake of security they are put in boiling 

 water for not more than half a minute. We may also 

 point out that experience has shown that boiling 

 the tubes, is not very good for them, for they easily 

 become too dense. After this, 2*5 c.c. of a i per cent, 

 solution of silk-peptone are poured into them ; the 

 tubes are again carefully rinsed in cold water, one 

 by one, and are then placed in Erlenmeyer flasks filled 

 with 20 c.c. of sterilized distilled water (compare 

 pp. 150-152). The latter is covered with toluol. In 



