PHLOGISTON. An old chemical name for an imaginary substance, supposed to be a combination of fire with some other matter, and a constituent part of all inflammable bodies, and of many other substances. See note, page 359.

PHOSPHATES. Salts formed by the combination of any base with phosphoric acid. See page 224.

PHOSPHITES. Salts formed by the combination of any base with phosphorous acid. See page 226.

PHOSPHURETS. Substances formed by an union with phosphorus. Thus we have phosphuret of lime, phosphuretted hydrogen, &c. See page 264.

PLUMBAGO. Carburet of iron, or the black lead of commerce. See page 278.

PNEUMATIC. Any thing relating to the airs and gases.

trough. A vessel filled in part with water or mercury, for the purpose of collecting gases, so that they may be readily removed from one vessel to another. See the last note, page 56.

PRECIPITATE. Any matter which, having been dissolved

in a fluid, falls to the bottom of the vessel on the addition of some other substance capable of producing a decomposition of the compound, in consequence of its attraction either for the menstruum, or for the matter which was before held in solution.

PRECIPITATION. That chemical process by which bodies dissolved, mixed, or suspended in a fluid, are separated from that fluid, and made to gravitate to the bottom of the vessel.

PRINCIPLES OF BODIES. Synonymous with Elements ; which see.

PRUSSIATES. Salts formed by the combination of any base with prussic acid. See page 233.

PUTREFACTION. The last fermentative process of nature,

by which organized bodies are decomposed so as to separate their principles, for the purpose of reuniting them by future attractions, in the production of new compositions.

PYRITES. An abundant mineral found on the English coasts, and elsewhere. Some are sulphurets of iron, and others sulphurets of copper, with a portion of alumine and silex. The former are worked for the sake of the sulphur, and the latter for sulphur and copper. They are also called Marcasites and Fire-stone.

martial. That species of pyrites which contains iron for its basis. See a full account of these minerals in Henckel's Pyritologia.

PYROMETER. An instrument invented by Mr. Wedgwood for ascertaining the degrees of heat in furnaces and intense fires. See Philosophical Transactions, vol. lxii. and ixiv. and Chemical Catech. note, page 81.

PYROPHORI Compound substances which heat of themselves, and take fire on the admission of atmospheric air. See an account of a variety of experiments with these compositions in Wiegleb's Chemistry, quarto, page 622, &c.

Q.

QUARTATION. A term used by refiners in a certain operation of parting. See Lewis's Com. Tech. page 135. QUARTZ. A name given to a variety of siliceous earths, mixed with a small portion of lime or alumine. Mr. Kirwan confines the term to the purer kind of silex. Rock crystal and the amethyst are species of quartz.

R.

RADICALS. A chemical term for the Elements of bodies; which see.

compound. When the base of an acid is composed of two or more substances, it is said that the acid is formed of a compound radical. The sulphuric acid is formed with a simple radical; but the vegetable acids, which have radicals composed of hydrogen and carbon, are said to be acids with compound radicals.

REAGENTS. Substances which are added to mineral waters or other liquids as tests to discover their nature and composition. See Test.

REALGAR. Red sulphuretted oxide of arsenic.

RECEIVERS. Globular glass vessels adapted to retorts for the

purpose of preserving and condensing the volatile matter raised in distillation.

RECTIFICATION, is nothing more than the re-distilling a

liquid to render it more pure, or more concentrated, by abstracting a part of it only.

REDUCTION. The restoration of metallic oxides to their original state of metals; which is usually effected by means of charcoal and fluxes. See page 367.

REFINING. The process of separating the perfect metals from other metallic substances, by what is called cupellation. See page 366.

REFRACTORY. A term applied to earths or metals that are either infusible, or that require an extraordinary degree of heat to change or melt them.

REFRIGERATORY. A contrivance of any kind, which, by containing cold water, answers the purpose of condensing the vapour or gas that arises in distillation. A wormtub is a refrigeratory.

REGISTERS. Openings in chimneys, or other parts of chemical furnaces, with sliding doors, to regulate the quan

tity of atmospheric air admitted to the fire-place, or to open or shut the communication with the chimney at pleasure. REGULUS. In its chemical acceptation, signifies a pure metallic substance, freed from all extraneous matters. REPULSION. A principle whereby the particles of bodies are prevented from coming into actual contact. It is, thought to be owing to caloric, which has been called the repulsive power. See chap. xiii. page 402. RESIDUUM. What is left in a pot or retort after the more

valuable part has been drawn-off. Thus the sulphate of potass which remains in the pot after the distillation of nitrous acid is called the residuum. It is sometimes called the caput mortuum.

RESINS. Vegetable juices concreted by evaporation either spontaneously or by fire. Their characteristic is solubility in alcohol, and not in water. It seems that they owe their solidity chiefly to their union with oxygen.

RETORT. A vessel in the shape of a pear, with its neck bent downwards, used in distillation; the extremity of which neck fits into that of another bottle called a receiver.

REVERBERATORY. An oven or furnace in which the flame is confined by a dome which occasions it to be beat down upon the floor of the furnace before it passes into the chimney. Some are so contrived that it returns or reverberates upon the matter under operation. REVIVIFICATION. See Reduction, which is a synonymous term: though" revivification" is generally used when speaking of quicksilver.

ROASTING. A preparative operation in metallurgy to dissipate the sulphur, arsenic, &c., with which a metal may be combined.

ROCK-CRYSTAL. Crystallized silex. See page 117.

S.

SACCHOLATES. Salts formed by the combination of any base with saccholactic acid. See page 201.

SALIFIABLE BASES. All the metals, alkalies, and earths, which are capable of combining with acids, and forming salts, are called salifiable bases.

SALINE. Partaking of the properties of a salt

SALTS neutral. A class of substances formed by the combination to saturation of an acid with an alkali, an earth, or other salifiable base.

-triple. Salts formed by the combination of an acid with two bases or radicals. The tartrate of soda and potass (Rochelle salt) is an instance of this kind of combination.

SANDIVER. A matter, composed of different salts, which rises as a pellicle on the surface of the pots in which glass is melted. It is used as a flux in the fusion of ores, and for other purposes. The term is probably a corruption of "Selle de verre."

SAP-COLOURS. A name given to various expressed vegetable juices of a viscid nature, which are inspissated by slow evaporation for the use of painters, &c.; sap-greef, gamboge, &c. are of this class.

SAFONACEOUS. A term applied to any substance which is of the nature or appearance of soap. See page 156. SATURATION. The act of impregnating a fluid with another substance, till no more can be received or imbibed. A fluid which holds as much of any substance as it can dissolve, is said to be saturated with that substance. A solid may in the same way be saturated with a fluid.

SEBATES. Salts formed by the combination of any base with sebacic acid. See page 205.

SELENITE. A salt existing in spring water, formed by sulphuric acid and lime. Its proper chemical name is Sulphate of Lime. See note, page 243.

SEMI-METAL. A name formerly given to those metals which, if exposed to the fire, are neither malleable, ductile, nor fixed. It is a term not used by modern

chemists.

SILICEOUS EARTHS. A term used to describe a variety of natural substances which are composed chiefly of silex; as quartz, flint, sand, &c.

SIMPLE SUBSTANCES. Synonymous with Elements; which see. See also page 249.

of

SMELTING. The operation of fusing ores for the purpose separating the metals they contain, from the sulphur and arsenic with which they are mineralized, and also from other heterogeneous matter.

SOLUBILITY. A characteristic of most salts. See Solu tion. See also page 239.

SOLUTION. The perfect union of a solid substance with a fluid. Salts dissolved in water are proper examples of solution.

SPARS. A name formerly given to various crystallized stones; such as the fluor spar, the adamantine spar, &c. These natural substances are now distinguished by names which denote the nature of each.

SPECIFIC GRAVITY. See the word Gravity.
SPELTER.

The commercial name of zinc.

SPIRIT. A term used by the early chemists to denote all volatile fluids collected by distillation.

proof. A term made use of to describe such ardent spirits as are of the same strength as the brandy of commerce, or of the specific gravity of 0.930, water being 1.000.

STALACTITES. Certain concretions of calcareous earth found suspended like icicles in caverns, They are formed by the oozing of water, through the crevices, charged with this kind of earth. See note, page 117. STEATITES. A kind of stone composed of silex, iron, and magnesia. Also called French chalk, Spanish chalk, and soap-rock.

STRATIFICATION. A chemical operation by which bodies are placed in a condition to act mutually upon each other by being arranged layer by layer, stratum super stratum, as is practised by metallurgists.

SUB-SALTS. Salts with less acid than is sufficient to neutralize their radicals. See page 215.

SUBERATES. Salts formed by the combination of any base with the suberic acid. See page 232.

SUBLIMATE. A name given to several mercurial prepara/tions.

SUBLIMATION. A process whereby certain volatile sub

stances are raised by heat, and again condensed by cold into a solid form. Flowers of sulphur are made in this way. The soot of our common fires is a familiar instance of this process. See Flowers.

SUCCINATES. Salts formed by the combination of any base with the succinic acid. See page 202.

SUGAR.

A well-known substance, found in a variety of vegetables, composed of oxygen, hydrogen, and carbon. See page 274.

SULPHATES. Salts formed by the combination of any base

with the sulphuric acid. SULPHITES. Salts formed by with the sulphurous acid.

See page 216.

the combination of any base See page 218.