3833. Goniometer

3833. Goniometer. An instrument used for measuring the angles of crystals. The only accurate and simple instrument of this kind is the reflective goniometer invented by Dr. Wollaston.

3834. To Filter Vegetable Juices

3834. To Filter Vegetable Juices. These should bo allowed to deposit their fecu-lous matter before filtration. The supernatant liquid will often be found quite clear; when this is not the case, filtration will be necessary through coarse filtering paper. (See No. 17 (Filtration).) Some vegetable juices can bo made clear simply by heating them to 180° to 200° Fahr., by which their albumen becomes coagulated.

Others admit of clarification in the same manner as syrups. (See No. 1357 (Clarification of Sugar for Syrups).) Many of these, again, such as hemlock, henbane, aco nite, etc., are greatly injured by heat, and must be filtered or decanted after repose.

3835. To Filter Vegetable Infusions

3835.    To Filter Vegetable Infusions. In many instances vegetable infusions and decoctions may be clarified by defecation and decantation of the clear liquid. A convenient method of straining, when that is necessary, is by securing the corners of a square piece of flannel to a frame, which can be laid over the mouth of a pan; or by laying the flannel across the mouth of a coarse hair-sieve. Concentrated infusions and decoctions, being usually weak tinctures, may be filtered as tinctures. (See No. 17 (Filtration).) Viscid vegetable solutions may be clarified (see No. 1357 (Clarification of Sugar for Syrups)); or may be made to filter rapidly by the addition of acetic, sulphuric, or other strong acid.

3836. To Filter Corrosive Liquids

3836.    To Filter Corrosive Liquids. Strong acids, etc., are filtered through powdered glass or siliceous sand, supported on pebbles in the throat of a glass funnel, or through asbestos placed in the same manner.

3837. To Filter Precipitates

3837.    To Filter Precipitates. When filtration is employed to separate precipitated matter from the solution in which it is suspended, the filtering medium should be such that the powder may be easily reclaimed from it with as little loss as possible. Linen or smooth bibulous paper are the best for this purpose. A camel-hair pencil should be used, if needed, in preference to a knife, to remove adhering powder from a filter, and the precipitate should be first washed down the sides of the filter by a small stream of water, so as to collect the most of it to one spot at the bottom.

The first runnings in filtration should always be returned to the filter.

3838. Bunsen's Method of Rapid Filtration

3838.     Bunsen's Method of Rapid Filtration. A great deal of time is frequently lost in washing precipitates, by having to wait for the liquid to pass through a filter. Bunsen's improvement consists in fixing the filtering funnel air-tight, by means of a perforated cork in the neck of a bottle which has an opening connected with the receiver of an air-pump. By exhausting the air in the bottle, the liquid will run faster through the filter in proportion to the diminution of the pressure in the bottle. Comparative experiments, some made according to the old, and others according to the new method showing that the filtration, washing, and drying of a precipitate, which took 7 hours by the old plan, could bo performed, by filtration into an exhausted bottle, in 13 minutes.