FILTERING AGAR-AGAR 131 



At the end of a half-hour the boiling mass may be easily 

 and quickly filtered through a heavy, folded paper filter 

 at the room temperature; as a rule the filtrate is as clear and 

 transparent as agar-agar usually appears. 



It may be well to emphasize the fact that for the filtration 

 of agar-agar no special device for maintaining the tem- 

 perature of the mass, is necessary. Agar-agar prepared 

 after the methods just given should pass through a properly 

 folded paper filter at the rate of a liter in from twelve to 

 fifteen minutes. 



Another plan that insures complete solution of the agar- 

 agar without causing the precipitates often seen when all 

 the ingredients are added at once and boiled for a long time 

 is to weigh out the necessary amount of agar-agar, 10 or 15 

 grams, and place this in 1300 or 1400 c.c. of water and boil 

 down over a free flame to 1000 c.c. The peptone, salt, and 

 beef extract are then added and the boiling continued until 

 they are dissolved. The clarification with egg-albumen may 

 then be done, and usually the mass filters quite clear and 

 does not show the presence of precipitates upon cooling. 

 If the mixture is positively alkaline, it is not only cloudy, 

 but it filters with difficulty; if it is acid, it is usually quite 

 clear, and filters more quickly, but, as Schultz has pointed 

 out, it loses at the same time some of its gelatinizing 

 properties. 



Another method by which agar-agar can be easily and 

 quickly melted is by steam under pressure. If the flask 

 containing the mixture of bouillon and agar-agar be kept 

 in the digester or autoclave for ten minutes with the steam 

 under a pressure of about one atmosphere, as shown by the 

 gauge, the agar-agar will be found at the end of this time 

 completely melted, and filtration may then be accomplished 

 with but little difficulty. 



