Sept. 12, 1884.] 



♦ KNOWLEDGE 



219 



have reserved this type of filter for our final example, 

 ina-smuch as it will help us to explain in detail what a 

 thoroughly good household filter ought to be. Water 

 suitable for drinking and cooking should be free from taste 

 and smell, yet so aerated and cool as to become refreshing. 

 It is needless to say that it ought also to be not only free 

 from harmful matters, but more, its administration should 

 be beneficial. The commonest impurities that are met with 

 in waters are adventitious particles derived from the earth 

 or its atmosphere ; they are more or less of appreciable 

 dimensions, and include such matters as the silt and other 

 detritus of streams, and organic matter, both Jiving and 

 dead. There are also other impurities of a less evident 

 nature, derived from both living and inert matter dissolved 

 in the water ; so that the requirements of a perfect filter 

 are twofold : it should be an eflicient mechanical strainer as 

 well as a chemical separator. Nor is this all ; it must 

 conform to the peculiar senses of man ; to his organs of 

 taste, his eye, and — if the truth must be written — to his 

 pocket. 



We insist at the beginning that the domestic filter 

 shall be " a thing of beauty," even though it be made of 

 such a homely substance as brown stoneware. Placed upon 

 the sideboard, chiflbnier, or other stand, the tap should be 

 at a convenient distance from the surface of the table, so 

 as to permit of the easy insertion of a tumbler beneath it, 

 as shown at Fig. 29. Such pedestals, we are glad to find. 



Fig. 29.— Maignen's Re- 

 frigerating Stand, with 

 "Filtre Kapide" and Ball- 

 valve attached. 



Fig. 30. — Sectional view of the 

 "Filtre Rapide." A, unfiltered 

 water ; B, screen ; c, granular " carho 

 calcis" ; D, powdered " carbo calcis" ; 

 E, asbestos cloth ; M, filtering frame ; 

 K, reservoir. 



are supplied by !Mr. Maignen ; and we notice with pleasure 

 that he has turned the pedestal to account to serve as a 

 " refrigerating stand," Fig. 29, where the filtered water is 

 made to pass through a non-oxidisable tin pipe imbedded in 

 ice — a most delightful luxury for the summer months. 



The filter-case ought to be constructed in such a way as 

 to permit of being taken to pieces, and the shapes of the 

 component parts such as to allow of their being easily and 

 thoroughly cleansed. It is but our duty to state that Mr. 

 P. A. Maignen must always be associated with this most 

 important advance in the structure of filter-cases as its 



originator, and we may point to Fig. 30 as substantially a 

 perfected model We need not here enter into a detailed 

 explanation of Mr. Maignen's filter-case, as we have already 

 done so in a former issue. Those of our readers, however, 

 who cannot have access to our previous brochures, and 

 who are desirous of learning something more about Mr. 

 Maignen's filter-case than the pictured description, Fig. 30, 

 would do well to write to him for a copy of his excellent 

 pamphlet on the filtration of water.* We may observe, 

 however, that the filtering mechanism consists of a funnel, 

 M, Fig. 30, the expanded portion of which is pierced by- 

 many circular apertures ; that oi-er this an asbestos cloth is 

 fitted ; and that the filtering medium is deposited uniformly 

 over the ichole of this surface. The idea of the asbestos 

 cloth and perforated funnel has, we find, been taken ad- 

 vantage of by another manufacturer, but, most unfortunately 

 for him, he has reversed the funnel and made a kind of a 

 bag of it; over the hollow cone the asbestos cloth is tied, 

 and the perforations in the funnel are elongated slits ; 

 hence it is obvious that the filtering surface is only par- 

 tially available, and the filtered water is not properly 

 aerated, as in the filter-case Fig. 30, where the stem of the 

 funnel, suitably plugged with cotton wool, to prevent the 

 entry of disease-germs, allows a stream of purified air to 

 enter the reservoir of filtered water underneath. 



The asbestos- cloth surface is undeniably Mr. Maignen's 

 invention ; it is of such a nature, that a very fine powder, 

 such as the " carbo calcis," enters into association with it in 

 such a way as to form one of the most perfect strainers 

 known. The cloth is subjected for a prolonged time to an 

 intense heat, so as to thoroughly purify it ere it is sent out 

 with the filter, and in order to cleanse it after continued 

 use, Mr. Maignen directs that it ought to be washed, and 

 then roasted before a clear fire ; this can be done in any 

 kitchen. 



The filtering medium is termed carbo calcis, because it 

 is made of pure carbon and pure lime, combined by the 

 patented process. It is in such a fine state of division that 

 it has been estimated that one square inch, | inch thick, 

 contains over 200,000 square inches of adhesive or straining 

 surface. Thus, when spread over the asbestos cloth, it 

 ought to be capable of preventing ihe passage over of even 

 the smallest germs — e.g., excessively small Micrococci 

 measure only about -^^g inch in diameter, and other 

 Bacteria and Bacilli are proportionately larger ; even the 

 jtagella of Bacterium termo, i.e., the whip-like terminal 

 appeudicular organs of motion of the organism, measure 

 2 0*7 i"<=h in breadth.! 



Fig. 31.— A Tillage Filter House. 



Over the fine layer of powdered carbo calcis, D., Fig. 30, 

 a quantity of granular carbo calcis may be placed, as at C, 

 Fig. 30 ; this does not only arrest the coarser impurities in 



* " Water, Preventable Disease, and Filtration." By P. A. 

 Maignen. 22 and 23, Great Tower-street, London, E.G., 18S-1. 



t Dallinger, " Monthly Microscopical Journal," London, vol. xiv. 

 p. 105. 



