recovered by transferring the moist drug to the water-bath of the still, and distilling in the usual manner. If the waterbath percolater and still is used, it is unnecessary to transfer the drug, as the still top can be adjusted, heat applied, and the distillation completed without further trouble. The process of distillation is a very important one in pharmacy, and is much less employed than it should be. EVAPORATION. As applied to pharmacy, evaporation is the process by which, with the aid of heat, the volume of liquids or other substances may be reduced. It is employed for many purposes in the practice of pharmacy, and is so familiar to druggists that but little need be said regarding it in this article. The vessels used for evaporating should be broad and low, or shallow, to give a larger surface for the application of heat and the escape of vapor. Evaporating dishes are made of glass, iron (enameled or glazed), platinum, porcelain, tin, etc. Heat is applied in various ways for the purpose of evaporating by the ordinary methods, by water-bath, sand-bath, steam, heated air, etc. For rapid evaporation heat over an open fire or by means of steam is best, but for making many preparations, such as extracts, fluid extracts, etc., slower evaporation is necessary, that the preparation may not be injured by the heat. For this purpose the water-bath is the most convenient for druggists' use, as by it the heat can be regulated and maintained at any desired temperature. In large establishments the vacuum pan, which is still better for the purpose, is employed. The most serviceable, cheap, evaporating dish, is the ordinary granite-iron stove skillet, or frying pan. Any ordinary evaporating dish may be set in a vessel of water, which will answer as a water-bath. A sand-bath may be made by partly filling an iron basin with sand and setting the evaporating dish in it. For very slow evaporation, a warming closet may be made by fastening a box against the wall and heating it with a lamp * The water bath which forms a part of FENNER'S WATER-BATH AND STILL is very convenient for the purpose of evaporation. It is shown in the sectional view on page 22 by the vessels A and B. FENNER'S WATER-BATH PERCOLATOR see page 34, may also be used for the same purpose, it being necessary only to put the liquid to be evaporated into the percolator and leave off the cover. placed underneath a hole in the bottom, smaller holes should also be provided in the upper surface for the escape of vapor. This box can be so arranged with shelves that a number of evaporating dishes may be placed in it at the same time. FILTRATION. The process of separating insoluble matter from liquids, by means of any substance or medium which will prevent its passage, is called filtration. Filtration, as it is employed in pharmacy, is usually conducted by means of filtering paper contained in a conical receptacle called a funnel*, but larger operations are carried on by other contrivances which will admit of more rapid filtration. The process of filtration is so familiar that it needs no explanation, but a few suggestions are here made for the benefit of the inexperienced. In filtering a liquid which contains a precipitate (unless the precipitiate is designed to clear the liquid, as magnesia or pumice stone are used) the liquid should be poured carefully off and filtered first, the precipitated portion being added after most of the liquid has passed through the filter; this makes the process more rapid. The first portion that passes through the filter should be returned to it and refiltered, as, when the filter is dry, it admits of the passage of small particles which are retained when its fibers have had time to swell by the absorption of moisture. In filtering liquids containing albuminous or gummy pre*FENNER'S SPIRAL FILTER RACK is a convenience for keeping the filtering paper off the sides of the funnel when filtering. It is made of tinned steel wire, of different sizes to fit different size funnels. It is simple, cleanly, durable, efficient, and cheap. The cut shows it as it is adjusted in the funnel ready for use. Heat often assists the process of filtering heavy liquids or oils. It may be conveniently applied by putting a filter inside of Fenner's water-bath percolator, and applying heat by means of the water-bath. For supporting the funnel during filtration, Fenner's Funnel Rack, which is shown in the cut, is very convenient. Further remarks on filtering will be found in the article on Economy and Filtering, page 32. cipitates it is also advantageous to put a coarse cotton cloth strainer on the inside of the filter paper, this catches the precipitate which may be removed with it, or in which it may be pressed to strain out the liquid, and thus makes the filtration more rapid. A plaited filter is generally used, except when a filter rack is employed, then the ordinary folded (quartered) filter is used. Besides filtering through paper, other means are often employed by druggists. Syrups and heavy liquids may be filtered through a flannel or cotton strainer, or felt filters that are made expressly for this purpose. Charcoal and sand in alternate layers are employed for filtering light liquids, when larger quantities are to be filtered. A little charcoal in powder, or powdered pumice stone sprinkled in the filter, will often assist to clear preparations that are difficult to filter clear. FINENESS OF POWDER. To properly obtain the soluble constituents of drugs by the process of percolation, they should be so comminuted or divided that the menstruum may readily dissolve all soluble matter. To this end, different drugs are directed to be reduced to different degrees of fineness as experience has shown to be best suited to their nature. The United States Pharmacopoeia has adopted the following standard for the fineness of powders : A coarse powder should pass through a sieve having 60 mesh- equals No. 60 powder. es to the linear inch, should pass through a sieve having 50 mesh-equals No. 50 powder. es to the linear inch, should pass through a sieve having 40 mesh-equals No. 40 powder. es to the linear inch,, should pass through a sieve having 20 mesh-equals No. 20 powder. es to the linear inch, Other degrees of fineness than the foregoing are often directed. It is desirable for the purpose of percolation that the powder used should be as uniform as possible, it is therefore directed in the Pharmacopeia that "not more than a small proportion of the powder should be able to pass through a sieve having ten meshes more to the linear inch." While this direction is valuable for securing a uniform powder and thereby promoting the process of percolation, it is, in our opinion, unwise to specify this limit; for in reducing drugs to different fineness of powder by any process which druggists may command, it is obvious that unless the powder is very fine quite a proportion of it will be much finer than the coarsest powder which will pass through the sieve having the required number of meshes to the inch. If this portion is separated from the coarser powder by sifting, that which remains will not truly represent the entire substance of the drug from which it was prepared. In preparing a powder, therefore, for percolation, the entire quantity of drug which is taken should be reduced to a powder that will pass through a sieve having the required number of meshes; or, if this produces a powder too fine for successful percolation a coarser sieve should be used, for it is better to use a coarser powder than to remove any portion of the drug which would be represented by the finer powder. For the reasons stated the powders directed in the formulæ of the U. S. P., are, as a rule, too fine for successful percolation by the majority of druggists, and better results will be secured by using about one grade coarser powder than is designated. Drugs are usually reduced to the required degree of fineness for percolation by grinding in a drug mill, but when finer powders are required the old, time-honored mortar and pestle comes into play. But few druggists, however, attempt to make what are known in the market as "powdered drugs. They are usually bought of reliable houses who make a business of putting them up. Drugs "ground for percolation" may also be bought in the market, but as they always come in bulk without the guarantee of a reliable house, they are liable to adulteration, and it is much better for the druggist to grind them himself, as needed, from reliable crude drugs. MACERATION. When percolation came to be the officinal process for exhausting drugs, maceration, the process of our forefathers, was mostly abandoned, but we are glad to see that in the present pharmacopoeia its value is again recognized, and that many preparations, which have of late been made by percolation, are now again made by maceration. In addition to this, the new pharmacopoeia, in making most of the tinctures, and some extracts gives the very much needed direction to macerate 24 hours with a portion of the menstruum before packing in the percolator. Maceration is the necessary primary step to successful percolation. It softens the drug, dissolves its soluble properties and loads the menstruum with them, ready to be carried away by the subsequent process of percolation. Whenever percolation is employed, sufficient time should be given for maceration to loosen and dissolve the soluble properties of the drug. If alcohol is the menstruum employed, the maceration may be conducted after packing the percolator, but if water forms a portion of the menstruum, the drug should first be macerated with a portion of the menstruum, sufficiently long to allow it to swell before it is packed in the percolator. Any convenient covered vessel may be used for macerating drugs designed to be percolated. For small quantities, glass, specie or salt mouth jars, or covered granite-ware stew-pans, are very convenient, even tin cans will not be injurious for most drugs. Drugs to be thus macerated should be thoroughly moistened with a portion of the menstruum and covered to prevent exposure and evaporation. When preparations are prepared entirely by maceration, the drugs should be put in a suitable glass jar or vessel, the menstruum added, and be frequently agitated for several days. PERCOLATION. The directions for percolation are much more complete and minute in the present, than in the former, revision of the pharmacopoeia, they are therefore repeated in full. "The process of percolation or displacement directed in this (1880) Pharmacopoeia consists in subjecting a substance or substances in powder contained in a vessel called a percolator, to the solvent action of successive portions of menstruum, in such a manner that the liquid as it traverses the powder in its descent to the recipient, shall be charged with the soluble portion of it, and pass from the percolator free from insoluble matter. "When the process is successfully conducted, the first portion of the liquid or percolate, passing through the percolator will be nearly saturated with the soluble constituents of the substance treated; and if the quantity of menstruum be sufficient for its exhaustion, the last portion of the per |