Polytechnic Association Pboceddings. . 965 



a further discussion of the suhject at this meeting. When Mr. 

 Andrews has accomplished his great task, and given to the world 

 his system in print, a discussion here on the soimdness of each new 

 proposition advanced, would doubtless be productive of some good. 



FILTERING APPARATUS. 



INIi'. John P. Gruber exhibited his filtering apparatjis, and gave a 

 practical demonstration of its operation. 



The annexed engraving represents air-pumps, in connection with a 

 rectifying or filtering apparatus. In it is seen an air-pump fastened 

 to a support, a barrel supposed to contain liquid of any description, 

 a stand on which rests the filtering apparatus, and another barrel 

 to receive the liquid after being filtered. * The filtering apparatus 

 consists of a metal cup or receiver, at the bottom of which is placed, 

 inside, a fine tin strainer, and on this is placed felt, filtering paper 

 or other material. At the bottom of the cup is a funnel, which 

 admits of the whole apparatus being placed in a circlar opening, 

 as the bung-hole of a barrel. It is kept tight by having the conical 

 part of the funnel covered with rubber. The filtering process is 

 as follows: The air-pump, working both ways, forces the air when 

 downward strokes are given, and exhausts the air when upward 

 stroke are taken. The hose connections between the barrels are 

 for exhausting or forcing the air, and conveying the liquid from 

 one vessel to another. The air is exhausted from the receiver, and 

 a vacuum is formed, at the same moment air is forced into the 

 barrel containing the liquid, and conseqently, with a pressure on 

 the surface of the liquid in one barrel, and a vacuum in the receiver, 

 the fluid flows from one vessel to the other, leaving all impurities 

 and muddy ingredients in the rectifier. The hose-pipe from the 

 side of the air-pump conducts the forced air to the barrel contain- 

 ing the liquid to be filtered. The pipe attached to the faucet 

 conveys the liquid to the receiver, leaving behind all impurities 

 during the passage through the rectifier. 



The inventor applies a similar apparatus to glass jars and bottles, 

 and being portable, it is useful to assayers, chemists and druggists. 

 The process of filtering is by this arrangement greatly expedited, 

 and in. the case of purifying volatile liquids, this is a matter of 

 some moment, as there is little loss by evaporation. After some 

 favorable criticism of this machine, the Association adjourned. 



