CERATA-(Cerates). Cerates (cera, wax) are a class of preparations similar to ointments, but of a firmer consistence. They are made by mixing oil or lard with wax, or some other substance having a higher melting point, imparting to them a consistency between that of an ointment and plaster. When applied to the skin they do not melt like ointments, but retain their soft consistence. The materials selected (oil or lard) should be free from all traces of rancidity. The wax or materials of higher fusing point should be first melted on a water-bath, then the oil or lard added in portions; when all is liquefied, the fluid should be stirred constantly while cooling, and those portions which congeal on the sides of the vessel re-incorporated until the whole assumes the proper consistence. Cerates should be kept in a cool place, in clean and well-covered jars. Those made with white wax, owing to its incipient rancidity, are liable to become rancid, while those containing yellow wax keep unaltered. Cerates are employed chiefly as dressings for inflamed surfaces. Steatins.*-These are a class of preparations which have the consistence of cerates, and contain suet combined with wax or lead plaster as base. The U. S. Pharmacopoeia recognizes 6 Cerates. Ceratum, Ceratum Cantharidis, Ceratum Cetacei, Spermaceti Cerate, Ceratum Plumbi Subacetatis, Ceratum Resinæ, . Basilicon Ointment, White Wax, 300 Gm.; Lard, 700 Gm. Camphor Liniment, 100 Gm., White Wax, 300 Gm.; Lard, 600 Gm Cantharides pulv., 320 Gm.; Yellow Wax, Spermaceti, 100 Gm.; White Wax, 350 Gm.; Solution of Lead Subacetate, 200 Gm.; Cam- Resin, 350 Gm.; Yellow Wax, 150 Gm.; Lard, 500 Gm. * Proposed by Mieleke, Phar. Centralhalle, 1881, Nos. 20-21. EMPLASTRA-(Plasters). PLASTERS are compounds of various fusible solids of a melting point higher than that of the human body, being friable when cold, but rendered adhesive by the warmth of the body. According to the base employed, they may be designated as Plasters proper, or as Resinous Plasters. Emplastrum Plumbi forms the base of the former class, while the latter consist of various combinations of resins. The Pharmacopoeia recognizes two ready-spread plasters, namely, Emplastrum Ichthyocollæ and Emplastrum Capsici. In the preparation of plasters, care should be taken that no higher degree of heat be employed than that of the water-bath, otherwise decomposition of the volatile medicinal constituents might ensue. Some plasters are made by simply fusing the various constituents together; others require the admixture of various solids, which are added to the fused mass either in a state of fine powder, or in the condition of a smooth paste obtained by treatment with a proper solvent. While cooling, the mass should be well stirred to insure uniformity in composition. After preparation, the plaster mass is usually moulded into sticks or rolls, and wrapped in waxed or paraffin paper. When kept for some time the plaster mass becomes hard and brittle, due to the oxidizing influence of the air; it may be restored to its original plasticity by re-melting it, with the addition of a little oil. Owing to the introduction of the rubber base, the preparation of plasters has almost entirely fallen into the hands of the manufacturer; it is seldom that the dispenser is required to spread other than cantharides plaster. SPREADING OF PLASTERS.-Plasters are usually spread on either muslin or leather (sheepskin), which is cut to the necessary size and shape, from one-quarter to one inch being allowed all around for a margin. The piece of leather or muslin is then stretched *The Plaster-press, as shown in Fig. 355, page 321, is adapted for this purpose. evenly on a smooth surface, being held in position by means of thumb-tacks. Over this is laid the form (Fig. 366), made of thin card-board or heavy paper, cut of the desired shape and size, and this is secured firmly by means of thumb-tacks. Plasters of an ointment like consistence (like Emp. Cantharidis) may be readily spread in a cold condition by means of a spatula. The plasters proper, because of their friable nature, are first melted and then spread with a hot spatula.* Sufficient of the plaster-mass (for the surface required) is selected and cautiously melted in a porcelain capsule over a gas-flame; the melted mass is then allowed to cool until it is of a honey-like consistence and, The form shown in Fig. 365 is specially designed for this purpose. by means of a warm spatula blade, quickly and evenly spread over the surface. The mass should not be applied too hot, otherwise it will penetrate the leather or muslin. After the plaster is spread, the surface should appear even and smooth; if it is not, a hot spatula should be quickly passed over it. Care should be taken, while heating the blade, to remove all particles of plaster adhering to it, otherwise the surface of the plaster will become discolored. Before removing the paper, or cardboard frame, the hot edge of the spatula should be passed around the line of contact, so that, when the frame is removed, a smooth, sharp edge may be left. For spreading larger numbers of plasters, the operation may be facilitated by the employment of the plaster-block (Fig. 367). This consists of a rectangular block of hard wood, the upper surface of which is convex. To one end of the upper surface is attached, by means of a hinge, a sheet-iron frame with an opening of the size desired for the plaster. The muslin or leather of proper size is laid on the convex surface of the block; over this is secured the sheet-iron frame, then the necessary amount of melted and partly-cooled plaster is poured in the center, and by means of a heated (triangular-shaped or round) plaster iron (Fig. 368), it is spread uniformly over the surface, the excess of plaster being forced over on the edges of the frame. PERFORATION OF PLASTERS.-This is done to permit the escape of exhalations from the skin, also to enable the plaster to adapt itself better to the skin, and to adhere more firmly. Perforation of plasters is carried on by the manufacturers of plasters on the large scale, by means of specially constructed machinery. For the use of the apothecary the perforating machine of Lentz is particularly adapted (Fig. 369). An inexpensive perforating apparatus has been devised by Professor Remington (Amer. Jour. Phar., 1878, p. 171), which consists of a brass cylindrical wheel studded with steel punches, which is driven with some force across the surface of the plaster, resulting in perforating along the line of contact. The employment of a rubber mass, as a base, has practically superseded all others. Its advantages reside in its flexibility and adhesiveness at ordinary temperatures, and in its not requiring any heat in applying or removing. This base consists essentially of a mixture of rubber with certain resins (burgundy pitch and olibanum), variously medicated. This pliable and adhesive rubber base retains its soft consistence indefinitely, and yields its medicinal constituents readily when applied to the skin. EXPLANATORY. EMPLASTRUM PLUMBI (Lead Plaster).-When fats are treated with alkali hydrates or with a number of other metallic oxides, decomposition takes place, the fatty acids combining with the metals forming soaps, while the glycerin is set free. Those soaps whose base is either soda or potassa, are known as the "soluble,' while those whose base constitutes a metallic oxide, are known as "insoluble" soaps. To this latter class Lead Plaster belongs. It may be prepared in either of two ways, viz.: 1st. By the interaction between soluble soaps and lead salts, (page 287). NaCHO + Pb/C2H2O2 CHO = Pb C18H33O2 Lead Oleate. 2d. By the process of saponification* (U. S. P. process). 2C3H5 (C18H3O2)3 + 3PbO + 3H2O = 3Pb(C18H3O2)2 + 2CH(OH), Glycerin. Any oil which consists of nearly pure olein may be used for this purpose. The U. S. Pharmacopoeia recognizes 13 Plasters. * In the restricted sense, as employed here, saponification is the separation of fats into their respective acids and glycerin. Here, the fatty acids are liberated by the action of the litharge (in the presence of water), uniting with the lead and separating out as an insoluble soap. |