A dealer in wares used by chemists informed Casamajor that he had many inquiries concerning asbestos for filtering liquids in chemical analysis. Some chemists complain that they cannot get clear Solutions through asbestos, while others, who obtain clear solutions, find that their liquids filter altogether too slowly.
The method of making asbestos filters, by pouring a thin paste of this material over a perforated platinum disc, was first proposed by Casamajor in 1875, but he neglected to give directions concerning the preparation of asbestos, to make it fit for filtering liquids in chemical analysis. It now appears, however, that such directions would be found useful.
The kind of asbestos to use is a matter of some importance. He tried 3 kinds, which are sold by dealers in New York as "Canadian," "Italian," and "Australian." This last is less flexible than the other two, and consequently the fibres do not felt together and pack as closely on the perforated plate. Hence, liquids filter more rapidly, and the Australian is, on this account, preferable to the other two kinds. He was informed that the Canadian asbestos is the most soluble in acids, but has not verified the assertion.
Whatever may be the kind of asbestos used, the following is a process for obtaining, with little trouble, a quantity of the pulp in a fit state for filtration:
A coarse brass sieve is placed over a sheet of paper, and a handful of asbestos is rubbed pretty roughly over the sieve-cloth. This breaks it up in such a way that the smaller fragments pass through the meshes, and are deposited on the paper underneath. After a while, the portion which remains on the sieve-cloth is collected in one bundle, and rubbed again in the same manner, and the operation is repeated until a sufficient quantity has gone through. In a few minutes enough of the material is obtained to last for months.
As to the coarseness of mesh to use, Casamajor has used No. 10 sieve (10 openings to the inch) with satisfactory results. The sieve is best placed bottom up, so as to leave plenty of room under the cloth.
The next operation is to free the sifted material from dust and from the finest particles. This is easily accomplished by placing the asbestos, as obtained above, over another sieve of finer mesh (about No. 25 or No. 30), and stirring it while water is poured over the sieve. The first water which passes through is quite milky, but it gradually becomes clearer as the washing is continued. The washed asbestos it then put in a beaker glass, and boiled for about 1/2 hour with strong hydrochloric acid (about 1 part of fuming HCl to 4
The pulp, after this treatment, it poured over a perforated platinum plate placed in a funnel, and washed with distilled water until no acidity is shown by litmus paper. The pulp is then taken out of the funnel and strongly heated in a platinum dish. After letting it coot sufficiently, it may be placed in a wide-mouth bottle for future use. (Jour. Amer. Chem. Soc.)invented by E. E. Robinson, and described in the Chemical News. When large quantities of liquids, such as reagents, have to be filtered in the laboratory, it is often convenient to have some means by which the funnel filter may be kept filled. The handling of large bottles for the purpose of emptying the liquid into the filter is disagreeable and tiresome. By the arrangement shown, such labour is avoided and the liquid is at the same time silently but surely transferred to the filler.
Fig. 16G shows an improved method of supplying liquid to a funnel fitler.
To the longer limb of the siphon is attached a abort rubber tube. Operating vertically within the lower end of the tube is the narrow conical stem of a glass bulb float, in the bottom of which are 2 or 3 small lead shot or weights for the purpose of retaining the stem of the float in a vertical position.
As the liquid in the funnel Alters out, the glass bulb descends, which in torn opens the bottom of the surrounding rubber pipe and permits the liquid in the siphon to flow out, falling over the bulb. If the liquid from the siphon flows faster than that through the filter, the bulb rises, and by its conical form wedges against the inner lower periphery of the rubber pipe, plugging the same, and stopping the flow therefrom. By this means the funnel is kept constantly supplied until all the liquid in the upper bottle has been siphoned out. An important advantage of this arrangement is that when once started it can be left without attention until the filtration is completed.
Pig. 167 shows a very simple apparatus for filtering water. Take a glass tube about 1 yd. long and of 1/4-in. bore, and bend it twice at a rightangle, as shown, so that the longer leg long as the shorter.
To the shorter leg is fastened, by means of a perforated cork, a wider glass tube, about 4 3/4 in. long and J in. wide (inside); this tube is filled with absorbent cotton (freed from fat), a small piece of perfectly clean sponge being laid next to the cork, and a similar piece being used to close the other opening of the tube. In place of the narrow glass tube, a rubber tube may also be used. The apparatus is started like any other kind of siphon, and will be found to work well in all cases where the liquid is not too much loaded with suspended matters.
Dr. Ebermayer reports that he has found muslin, which is folded in shape of a filter, and placed below the latter, to be an excellent promoter of rapid filtration. He had occasion to make use of such additional muslin filters, for the purpose of removing the paper-filters from the funnel, without tearing; and he thereby had occasion to notice this useful property of the additional muslin filter. (New Remedies.)
It is known that certain precipitates, such as sulphur, in emulsion pass through filter paper. Boisbaudran often employs a method which in many cases obviates this inconvenience, and which, to his knowledge, has not yet been made public. Filter paper is boiled with aqua regia until the mass is fluidified; it is then poured into a large quantity of water, and the white precipitate formed is washed by decantation. To render the texture of a filter very compact, it is filled with this material, previously stirred up in water, so as to form a very thin paste, and allowed to drain. The paper is thus covered with a layer, which obstructs its pores. Or a little of the same pasty matter may be mixed with the liquid to be filtered.
Eiselt recommends the use of sponge for filtering distilled water. The filtration goes on with great rapidity, and the product is clear as crystal. When filtered through paper, distilled water soon exhibits a "felty" sediment, which is never formed when filtered through sponge, so that the bottles scarcely need cleaning after several months' use. The apparatus that he employs consists of a bottle with an opening near the bottom from which descends a bent glass tube. This tube is about 6 in. long and 1-1 1/2 in. in diameter; at each end is a perforated rubber stopper bearing a narrower glass tube. The wide tube contains one or two long strips of fine sponge that has been cleaned with dilute hydrochloric acid and then dried. The bottle to which this filter is attached must not be larger than the one placed beneath to catch the filtrate. The sponge, of course, must be cleaned every few months. (Neuste Erfah-rungen.)
G. F. Burton, of Springfield, Ohio, is the inventor and manufacturer of an appliance shown in Fig. 168, to be used in connection with an ordinary funnel or percolator, designed to prevent loss by evaporation and the escape of odours, and to exclude dust and flies. It will also serve as an air-tight cover to a macerating or infusion vessel. By the ordinary method of filtering and percolation one loses constantly by evaporation not only in alcohol, but often in the volatile portion of the drug: while to keep the filter or percolator supplied requires constant attention. If filled and left at night, in the morning the filtering paper will usually be dry and gummed, or the drug in the percolator be exposed to air. These difficulties are entirely overcome by this apparatus.
To use it, place the rubber stopper into the receiving bottle, and insert the funnel or percolator (previously packed). On this place the cover. Into a suitable discharge bottle containing the desired quantity of liquid, insert the cork with the rubber tube attached, closed by means of the pinch-cock. Secure this inverted, at a proper height, directly above the cover, and pass the rubber tube through it as far as is desirable, to permit the liquid to rise in the funnel or percolator. Press on the rubber of the cover to secure it firmly to the edge of the funnel or percolator. There should be a slight bend in the supply pipe, otherwise it mightdraw the cover out of place; if too much, there will not be a free flow of liquid. Loosen the pinch-cock, when the liquid will flow until it reaches the end of the tube and close it. Then no more will run until the liquid is low enough in the funnel or percolator to admit air, when mure will flow as before. Should the quantity of liquid be small, or for any other reason it is not desired to use the supply vessel, insert the stopper in place of the tube.
When the liquid begins to drop from the percolator, if it is desired to set it aside for a given length of time to macerate, instead of closing the lower orifice with a cork, the How may be stopped by closing the air-tube by means of the pinch-cock. The funnel or percolator should not exceed 8 1/2 in. in diameter. With this size, or a little smaller, a 7-in. filtering cock and No. 33 paper can be used. If it be desired to employ vessels the full size of the cover, to secure it perfectly tight, it may be necessary to weigh it down with sand, or by filling it with water.