FILTRATION. 79 



The employment of the hot-water funnel, so often 

 recommended, has been dispensed with in this work to 

 a very large extent, as we know that, if the solution 

 of the gelatin is complete, filtration is so rapid as not 

 to necessitate the use of an apparatus for maintaining 

 the high temperature. The temperature at which the 

 hot-water funnel retains the gelatin is so high that evap- 

 oration and concentration rapidly occur, and in conse- 

 quence the filtration is, as a rule, retarded. The filtra- 

 tion is frequently done in the steam sterilizer, but this 

 too is unnecessary if the gelatin is quite dissolved. At 

 the ordinary temperature of the room and by the means 

 commonly employed for the filtration of other sub- 

 stances, both gelatin and agar-agar may be rapidly fil- 

 tered if they are completely dissolved. 



It not infrequently occurs that, even under the most 

 careful treatment, the filtered gelatin is not perfectly 

 transparent (the condition in which it must exist, other- 

 wise it is useless), and clarification becomes necessary. 

 For this purpose the mass must be redissolved, and 

 when at a temperature between 60° C. and 70° C, the 

 whites of two eggs, which have been beaten up with 

 about 50 c.c. of water, are added. The whole is then 

 thoroughly mixed together and again brought to the 

 boiling-point, and kept at this point until coagulation of 

 the albumin occurs. It is better not to break up the 

 large masses of coagulated albumin if it can be avoided, 

 as when broken up into fine flakes they clog the filter 

 and materially retard filtration. 



The practice sometimes recommended of removing 

 these albuminous masses by first filtering the gelatin 

 through a cloth, and then finally through paper, is not 

 only superfluous, but in most instances renders the pro- 



