10 BULLETIN 1025, 0". S. DEPABTMENT OF AGBICTJLTTJBE. 



ployed retain traces of salts even after very prolonged washing on 

 a filter and can be purified only by dialysis. A portion of the ma- 

 terial forms quite stable susj^ension in a fruit juice to which it is 

 added, the precipitate forms very slowly, the removal of colloidal 

 matter is imperfect, and the filtration of a juice so treated is almost 

 impossible by reason of the prompt formation over the filtering 

 surface of a slimy, well-nigh impervious layer. Silicic-acid gels pre- 

 pared and purified by more exact methods also fail to give satisfac- 

 tory clarification or to filter readily. The preparation of the gel in- 

 volves too many difficulties, and its use yields results too far short 

 of satisfaction to make it a promising material for use in clarifying 

 fruit juices. 



DIATOMACEOUS EAETH (KIESELGUHR) AS A CLARIFYING AGENT. 



Diatomaceous ("infusorial") earth (kieselguhr) 2 has been recom- 

 mended as a filtering agent for various liquids, and patents covering 

 its use in clarifying cane juices were issued in both Great Britain 

 and the United States as early as 1886 (21, p. 586). Its use for the 

 purpose, either alone or in combination with other materials, has 

 been repeatedly suggested in the older literature. More recentty 

 there has been a decided revival of interest in kieselguhr as a clarify- 

 ing agent, as evidenced by a considerable number of papers and the 

 patenting of several processes. Gore (12) recommended its use as 

 an aid to the filtration of previously neutralized apple juice in making 

 apple sirup and also as an aid in filtering fresh apple juices through 

 a filter press (IS). More recently Peck and Adams (26) have de- 

 scribed a new carbon intended for use in clarifying cane juices, which 

 is made by mixing molasses with kieselguhr, treating with sulphuric 

 acid, baking, and washing free of acid. The material is reported to 

 have very great decolorizing power and to give very considerable in- 

 crease in purity with a reduction of gums to 30 to 45 per cent of the 

 amounts present before treatment, which would suggest, in view of 

 Zerban's results with carbons, that the kieselguhr aids very ma- 

 terially in the adsorption of gums. 



Peck (24) has reported results obtained by the addition of kiesel- 

 guhr to the juice at the rate of 5 pounds per ton of cane, with con- 

 siderable increase in purity. The same author in an address has 

 also made incidental mention (25) of the work of Walter L. Jordan 

 in filtering juices through kieselguhr, stating that an increase in 

 purity was obtained, but Peck gives neither details nor citation of 

 Jordan's paper, which it has been impossible to locate in the litera- 



2 Since kieselguhr consists chiefly or wholly of the siliceous frustules of diatoms, it 

 is unfortunate that the older and correct designations diatomaceous earth, diatomite, or 

 tri polite, which suggest the origin and chemical character of the material, should have 

 been replaced in trade usage by the wholly misleading term " infusorial earth." 



