=Plaster of Soap (Compound).= _Syn._ EMPLASTRUM SAPONIS COMPOSITUM, E.
ADHaeRENS, L. Prep. (Ph. D. 1826.) Resin plaster, 3 oz.; soap plaster, 2 oz.; melted together.
_Obs._ Less emollient, but more stimulant, than the simple plaster. The 'EMPLASTRUM e MINIO CUM SAPONE'--Ph. E. 1744 was made by melting 1 part of soap with 5 parts of minium plaster. Neither of the above must be put into water. See PLASTER OF RESIN, Ph. D.
=Plaster of Soap-ce'rate.= _Syn._ EMPLASTRUM CERATI SAPONIS (B. P.).
_Prep._ 1. From soap cerate, heated by means of a water bath until all the moisture is evaporated. Sometimes 2 or 3 dr. each of powdered mastic and gum ammoniacum are added for each pound of cerate. The product is generally spread whilst still warm. Said to be suppurative, resolvent, cooling, and desiccative. See CERATE (soap).
2. (B. P.) Hard soap, 10; beeswax, 12-1/2; oxide of lead (in powder), 15; olive oil, 20; vinegar, 160; boil the vinegar with the oxide over a slow fire, or by a steam bath, constantly stirring them until they unite; then add the soap and boil again in a similar manner until all the moisture is evaporated; lastly, mix with the wax previously dissolved in the oil, and continue the process till the product takes the consistence of a plaster.
=Plaster of Squill, Compound.= _Syn._ EMPLASTRUM SCILLae COMPOSITUM.
_Prep._ Galbanum, 1/2 oz.; soap, 1/2 oz.; litharge plaster, 2 oz.; melt together, and add opium, 1 dr.; ammoniacum, 1/2 oz.; vinegar of squills, 3 oz., mixed together; keep them over the fire constantly stirred till they are incorporated.
=Plaster, St Andrew's.= _Prep_. From yellow resin, 8 oz.; gum elemi, 2 oz.; Bordeaux turpentine and oil of the bay-laurel, of each 1 oz.; melted together by a gentle heat. A stimulant, resolvent, and adhesive plaster, once supposed to possess extraordinary virtues.
=Plaster, Stick'ing.= See PLASTER, COURT, PLASTER OF RESIN, &c.
=Plaster, Stom'ach.= See PLASTER, AROMATIC, &c.
=Plaster, Strength'ening.= See PLASTERS OF FRANKINCENSE and OXIDE OF IRON.
=Plaster, Styp'tic.= See PLASTER OF OXIDE OF IRON, PARACELSUS'S P., &c.
=Plaster of Sul'phate of Quinine'.= _Syn._ EMPLASTRUM QUINIae, E. Q.
DISULPHATIS, L. _Prep._ 1. Sulphate of quinine, 1 dr.; resin plaster, 1 oz. Applied to the abdomen in intermittents.
2. Sulphate of quinine, 1 dr.; mercurial plaster, 2 oz. In affections of the liver or spleen, following intermittents, applied over the regions of those viscera.
3. Resin plaster, 9 dr.; sulphate of quinine, 1 dr.; camphor and oil of cajeput, of each 1/2 dr. Applied over the epigastrium as a prophylactic of cholera.
=Plaster of Thus.= See PLASTER OF FRANKINCENSE.
=Plaster of Ver'digris.= Syn. EMPLASTRUM aeRUGINIS, E. CUPRI SUBACETATIS, L. Prep. (P. Cod.) Beeswax, 4 parts; Burgundy pitch, 2 parts; melt, add of Venice turpentine and prepared verdigris (in powder), of each 1 part, and stir until the mass is nearly cold. For other formulae, see PLASTER, CORN, &c.
=Plaster, Ver'mifuge.= _Syn._ EMPLASTRUM VERMIFUGUM, E. ANTHELMINTICUM, L.
Prep. From powdered aloes, 1 dr.; oil of chamomile, 10 drops; croton oil, 2 drops; oil of turpentine, q. s.
=Plaster, Vigo's.= _Syn._ EMPLASTRUM VIGONIS, L. _Prep._ (P. Cod.) Lead plaster, 40 oz.; mercury, 12 oz.; liquid styrax, 6 oz.; beeswax, turpentine, and resin, of each 2 oz.; ammoniacum, bdellium, myrrh, and olibanum, of each 5 dr.; saffron, 3 dr.; oil of lavender, 2 dr.; made into a plaster s.a.
=Plaster, Warm.= See CALEFACIENT PLASTER, BURGUNDY PITCH P., &c.
=Plaster of Wax.= _Syn._ SIMPLE PLASTER; EMPLASTRUM ATTRAHENS, E. SIMPLEX (Ph. E.), E. CERae, L. _Prep._ 1. (Ph. E.) Beeswax, 3 oz.; suet and yellow resin, of each 2 oz.; melt them together, and stir the mixture briskly until it concretes by cooling.
2. (Ph. L. 1836.) Yellow wax and suet, of each 3 lbs.; yellow resin, 1 lb.; as the last. Intended to be employed as a simple dressing, especially to blistered surfaces. It is now seldom used.
=Plaster, White Diach'ylon.= See PLASTER OF LEAD.
=Plaster, Yellow Diach'ylon.= See PLASTER OF GALBANUM.
=Plaster, Zinco-lead.= _Syn._ EMPLASTRUM ZINCO-PLUMBICUM, E.
DIAPOMPHOLYGOS, L. _Prep._ (Ph. Suec.) Beeswax, 1 lb; olive oil and graphite (black lead), of each 6 oz.; carbonate of lead, 4 oz.; oxide of zinc (impure), 3 oz.; olibanum, 1-1/2 oz.; boil to a plaster. Astringent and desiccant. Other forms substitute an equal weight of litharge for the graphite.
=PLATE.= The name is commonly given to gold and silver wrought into instruments or utensils for domestic use.
The cleaning of plate is an important operation in a large establishment, as its durability, and much of its beauty, depend on this being properly done. The common practice of using mercurial plate powder is destructive to both of these, as mercury not only rapidly erodes the surface of silver, but renders it soft, and, in extreme cases, even brittle. The only powder that may be safely used for silver is prepared chalk, of the best quality. For gold, the form of red oxide of iron, known as _Jeweller's Rouge_, is the most useful and appropriate.
In his 'Workshop Receipts' Mr Spon recommends the following:--"Take an ounce each of cream of tartar, common salt, and alum, and boil in a gallon or more of water. After the plate is taken out and rubbed dry it puts on a beautiful silvery whiteness. Powdered magnesia may be used dry for articles slightly tarnished, but if very dirty it must be used first wet and then dry."
Chamois leather, a plate brush, or very soft woollen rags, should alone be used to apply them; and their application should be gentle and long continued, rather than the reverse. Dirty plate, after being cleaned with boiling water, may be restored by boiling it in water, each quart of which contains a few grains of carbonate of soda, and about an ounce of prepared chalk, calcined hartshorn, or cuttle-fish bone, in very fine powder. The ebullition sets up a gentle friction, which effects its purpose admirably.
The boiled plate, after being dried, is best 'finished off' with a piece of soft leather or woollen cloth which has been dipped into the cold mixture of chalk and water, and then dried. The same method answers admirably with German silver, brass, pewter, and all the softer metals.
See POWDER (Plate), &c.
=PLAT'INA.= See PLATINUM.
=PLA"TING.= The art of covering copper and other metals with either silver or gold.
Plating is performed in various ways. Sometimes the silver is fluxed on to the surface of the copper by means of a solution of borax, and subsequent exposure in the 'plating furnace,' and the compound ingot is then rolled to the requisite thinness between cylinders of polished steel. The common thickness of the silver plate before rolling is equal to about the 1-40th of that of the compound ingot. Sometimes the nobler metal is precipitated from its solutions upon the copper by the action of chemical affinity, or, more frequently, by the agency of electro-chemical decomposition (electro-plating).
The metal employed for plating is a mixture of copper and brass, annealed or hardened, as the case may require. For electro-plated goods, 'nickel silver' is now almost invariably employed. See ELECTROTYPE, GILDING, PLATINISING, SILVERING, &c.
=PLAT'INISING.= Metals may be coated with platinum by nearly similar processes to those already referred to under PLATING. In the 'moist way'
vessels of brass, copper, and silver are conveniently platinised in the following manner:--Solid bichloride of platinum, 1 part, is dissolved in water, 100 parts, and to this solution is added of common salt, 8 parts; or, still better, 1 part of ammonio-chloride of platinum and 8 parts of chloride of ammonium are placed in a suitable porcelain vessel, with about 40 parts of water, and the whole heated to ebullition; the vessels or utensils, previously made perfectly bright, are then immersed in the boiling liquid. In a few seconds they generally acquire a brilliant and firmly adhering layer of platinum.
Silver plates for voltaic batteries are commonly platinised by immersing them for a few seconds in a mixture of saturated solution of bichloride of platinum, 1 part; dilute sulphuric acid, 3 parts; water, 4 to 6 parts.
Platinum battery plates are covered with a pulverulent deposit of platinum by means of the electrotype.
Platinised asbestos is prepared by dipping asbestos into a solution of bichloride of platinum, or one of the double chlorides of that metal, and then gradually heating it to redness. It is used as a substitute for spongy platinum. See ELECTROTYPE, VOLTAIC ELECTRICITY.
=PLAT'INUM.= Pt. _Syn._ PLATINA, WHITE GOLD; PLATINUM, L. A heavy, greyish-white metal, occurring chiefly in certain of the alluvial districts of Mexico and Brazil, in the Ural mountains of Russia, in Ceylon, and in a few other places. It occurs in nature under the form of grains and small rolled masses, associated with palladium, rhodium, osmium, ruthenium, iridium, and a little iron. It has only been known in Europe since 1748.
_Prep._ The native alloy of this metal (crude platinum) is acted upon, as far as possible, by nitro-hydrochloric acid containing an excess of hydrochloric acid, and slightly diluted with water, in order to dissolve as small a quantity of iridium as possible; to the deep yellowish-red and high acid solution thus produced ammonium chloride is added, by which nearly the whole of the platinum is thrown down in the state of ammonio-chloride. This substance, after being washed with a little cold water, is dried and heated to redness; the product is spongy metallic platinum. This is made into a thin uniform paste with water, introduced into a slightly conical mould of brass, and subjected to a graduated pressure, by which the water is squeezed out, and the mass rendered at length sufficiently solid to bear handling. It is next dried, very carefully heated to whiteness, and hammered, or subjected to powerful pressure by suitable means, whilst in the heated state. It will now bear forging into a bar, and may afterwards be rolled into plates, or drawn into wire, at pleasure.
_Prop., &c._ Platinum is one of the heaviest substances known, its sp. gr.
being 215. It is whiter than iron, harder than silver, infusible in the strongest heat of our furnaces, and melts only when exposed to the highest temperature obtained by Deville's oxyhydrogen gas furnace. It is unaffected by air, water, and all the ordinary acids, and even its polish is uninjured by the strongest heat of a smith's forge; aqua regia, however, dissolves it, though with much more difficulty than gold; it is also superficially oxidised by fused hydrate of potassium. Spongy platinum, powdered platinum, and even perfectly clean platinum foil, possess the remarkable property of causing the union of oxygen and hydrogen gases, with more or less elevation of temperature. Platinum is precipitated from its solutions by deoxidising substances under the form of a black powder (platinum black), which has the power of absorbing oxygen, and again imparting it to combustible substances, and thus causing their oxidation. In this way alcohol and pyroxylic spirit may be converted into acetic and formic acids, &c.
Platinum black is simply platinum in a fine state of division, and is readily obtained as follows:--1. A solution of platinic chloride, to which an excess of carbonate of sodium and a quantity of sugar have been added, is boiled until the precipitate which forms after a little time becomes perfectly black, and the supernatant liquid colourless; the black powder is then collected on a filter, washed, and dried by gentle heat.
2. Platinic-ammonium chloride, reduced to very fine powder, is moistened with strong sulphuric acid, and a small piece of zinc is thrust into the mixture; after the whole is reduced to a black powder it is washed, first with hydrochloric acid, and then with pure water, and is, lastly, dried.
3. (Zdrawkowitch.) Platinum black, in a highly active condition, can be obtained, according to the author, by adding 3 to 5 c.c. of solution of perchloride of platinum, drop by drop, to a boiling mixture of 15 c.c. of glycerin and 10 c.c. of solution of caustic potash of 108 sp. gr.
4. (Ph. B.) Boil down rapidly, solution of potash, 2 pints, in a silver or clean iron vessel, until there remains a fluid of oily consistence, a drop of which removed on a warm glass rod solidifies on cooling. Pour this into proper moulds, and when solidified and while still warm put it into stoppered bottles.
Platinum, in the state of platinum black, possesses the property of condensing gases, more especially oxygen, into its pores, and afterwards giving it out to various oxidisable substances. When placed in contact with a solution of formic acid it converts it, with copious effervescence, into carbonic acid; alcohol, dropped upon it, becomes changed by oxidation into acetic acid, the rise of temperature being often sufficient to cause inflammation; exposed to a red heat, it shrinks in volume, assumes the appearance of spongy platinum, and, for the most part, loses these peculiarities. That prepared with zinc explodes, when heated, like gunpowder. The spongy platinum is obtained by igniting the ammonium platinic chloride at a red heat.
The salts of platinum are recognised as follows:--Sulphuretted hydrogen throws down from neutral and acid solutions of the platinic salts a blackish-brown precipitate, which is only formed after a time in the cold, but immediately on heating the liquid. Ammonium sulphide also gives a blackish-brown precipitate, which completely redissolves in a large excess of the precipitant, provided the latter contains an excess of sulphur.
Chloride of ammonium and chloride of potassium give yellow crystalline precipitates, insoluble in acids, but soluble in excess of the precipitate, upon the application of heat, and decomposable by heat, with production of spongy platinum. Ammonia and potassium hydrate also give similar precipitates in solutions previously acidulated with hydrochloric acid.
_Estim._ This may be effected by throwing down the metal in the form of chloride of ammonium and platinum, which, after being washed on a filter with a little weak spirit to which a little of the precipitate has been added, and afterwards with the spirit alone, may be carefully dried at 212 Fahr., and weighed. Or, the precipitate may be ignited in a platinum crucible, and weighed in the state of a spongy platinum. 19325 gr. of the platinic and ammonium chlorides are equivalent to 9875 gr. of metallic platinum.