THE CLARIFICATION OF FRUIT JUICES. 9 



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 CLAKIFYING 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 

 HC1 or H 2 S0 4 , 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 this end. 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 HC1 or H 2 S0 4 , the precipitate consisted mainly of meta- 

 silicic acid, H 2 Si0 3 , with some orthosilicic acid, H 4 Si0 4 , containing 

 sulphates or chlorids of sodium or potassium. When ammonium 

 salts or NH 4 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 2 



