SYSTEMATICALLY SELECTED YEASTS. 69 



employed. By way of comparison, a Chamberland filter, a 

 porcelain tube marked with the letter F, was also examined. 

 The results obtained were as follows : 



I. Chamberland filter with one tube 



At i-ij atm. pressure, 20 cubic feet passed in one hour. 



2~<t > *4 )> 



,, about 10 



5 



II. Filter with 50 grams cotton-wool (about "32 gram 

 per cc.) 



At 3 atm. pressure, 120 cubic feet passed in one hour. 



I 15 



10 





,, about \ ,, about 7 ,, 



III. Filter with 35 grams cotton- wool (about *22 gram 

 per cc.) 



At atm. pressure 27 cubic feet passed in one hour. 



"3 ' *9 



M ? 12 



The reason that the above table does not contain more 

 results is that the measuring apparatus was only for a short 

 time at Mr. Poulsen's disposal. The numbers obtained, how- 

 ever, sufficiently Indicate the capabilities of the two kinds of 

 filters. On comparing these numbers it is seen that the 

 Chamberland filter and the filter containing 50 grams of 

 cotton-wool are about equal in their filtering capacity, but 

 that the filter containing 35 grams of cotton-wool consider- 

 ably excels them both in this respect. These experiments 

 were, of course, all carried out with the same measuring 

 apparatus. 



The air filters described above are not only used in con- 

 nection with the pure yeast propagating apparatus, but also 

 in the centrifugal apparatus of Bergh, and in Ritter's apparatus 

 for collecting the yeast. In a slightly modified form they are 

 also used in the Old Carlsberg apparatus, and in the similar 

 closed vessels which have been introduced during the last 

 few years in the place of the open coolers. 



