THE CLARIFICATION OF FRUIT JUICES. ) 
appears that such carbons as have been studied must be regarded as 
decolorizing agents rather than aS potentially valuable aids in clari- 
fying fruit juices. 
GELATINOUS SILICA AS A CLARIFYING AGENT. 
Deprax (9), in a brief popular note, has reported good results in 
the clarification of beers which had proved refractory to the usual 
fining with gelatin from the use of “ gelatinous silica ” prepared by 
precipitating an aqueous solution of an alkaline silicate by adding 
HC] or H,SO,, washing, filtering, and pressing. Though it is noted 
that certain conditions of concentration must be observed, these are 
not stated. The author also suggests that the process may be greatly 
simplified by the substitution of ammonia or ammoniacal salts for 
acids as precipitating agents, stating that the resulting mixture is as 
effective for clarifying purposes as the acid precipitate. Using 100 
grams of the gel, containing 17 grams of dry silicic acid per hecto- 
liter of beer, he reports that he obtains a relatively dense, rapidly 
formed, quick-settling precipitate. In exceptional cases, larger 
quantities are necessary, but Deprax states that large quantities 
might be used, since he has determined that the material is insoluble 
in the liquid. 
An extensive literature has grown out of Martin’s discovery (19) 
that colloids may be removed from their dispersion means by filtra- 
tion through a suitably supported layer of silicic-acid gel, and every 
textbook of colloid chemistry devotes considerable space to ultra- 
filtration through this and similar gels as a means to thisend. Little 
attention seems to have been given to the possibility of the use of 
silicic-acid gel as an adsorbing agent in the manner suggested by ° 
Deprax, and his note is the only record that it has been possible to 
find in the literature of an attempt to use it as a clarifying agent for 
beer or wine. 
Deprax (9) gives no details as to the preparation of his material; 
it is clear, however, that when sodium or potassium silicate was 
treated with HCl or H,SO,, the precipitate consisted mainly of meta- 
silicic acid, H,SiO,, with some orthosilicic acid, H,SiO,, containing 
sulphates or chlorids of sodium or potassium. When ammonium 
salts or NH,OH were employed as precipitants, the resulting mix- 
ture of silicic acids contained sodium and potassium salts or hydrox- 
ids together with free ammonia. Since Deprax prepared his mate- 
rial by washing, filtering, and pressing, it is certain that all these 
impurities were present in the respective preparations. : 
In the work done in the laboratory of the Bureau of Plant Indus- 
try it has been found impossible to produce satisfactory clarification 
with silicic-acid gels. Such crude preparations as Deprax em- 
71054°—22—_9 
