« VorigeDoorgaan »
and the stone is raised at one end, for the superfluous quicksilver to drain off: the whole of the tin-foil and quicksilver are incorporated, the weights are removed, and the mirror finished. Pins are made of brass wire, and blanched or silvered with a preparation of tin.
CHARLES. Is not tin an ingredient in pewter? MR. HARCOURT. Pewter is composed of tin, and other substances mixed with it. It was formerly much used for dishes and plates, but is almost banished by the general use of earthen-ware, which is cleaner, and pleasanter in every respect, except that of retaining heat, in which it is excelled by the pewter.
SOPHIA. Pewter has a great resemblance to lead, which, I think, is the next of which we are to treat.
MR. HARCOURT. Its colour is a little like it. Lead is a coarse, soft metal, but a very useful one. It is so soft and flexible, that it is easily cut with a knife; shaved with a plane; grooved for windows, by being drawn through the glazier's vice; or flatted into large thin sheets, by passing it between wooden rollers. It has less malleability than the other
metals we have already described; and no capacity of being drawn into wire, which arises from a want of tenacity. Lead is easily fused, and melts long before it becomes redhot: as soon as it becomes fluid, it calcines, and greyish ashes are formed upon its surface. When in a middle state between hot and cold, it is readily formed into small round grains. Thus, shot is made of it, by infusing a due proportion of yellow orpiment into it, and then pouring it through a plate of copper, bored with holes of a suitable size, like a colander, through which the liquid metal passes, and subsides in round balls or grains.
AUGUSTA. Pray what are the compositions which form red and white lead?
MR. HARCOURT. Red-lead is a preparation of the metal whose name it bears, by calcination, and long exposure to a strong flame. White-lead is formed of its calx, obtained in the fume of vinegar. All acids have the power of dissolving it. This last is of great service to the painters, both in oil and water colours. The discovery of a substitute for it, in house-painting especially, is much to be
desired, on account of its extremely pernicious qualities to the health of the workmen who use it. It is also an ingredient in cosmetics, for beautifying the complexion; but when it is brought into contact with any water or air that contains sulphur, it is instantly changed from a delicate white to a very dirty and dark brown; and this is a distinguishing character of lead. When salt of tartar is heated red hot in a ladle, and a little sulphur is added to it, it forms a compound that possesses the useful quality of detecting lead in any of its solutions, and may be tried upon Goulard's extract.
MRS. HARCOURT. The custom of painting the face becomes those only who have effaced the native hues of youth by late hours and high living; but is entirely inconsistent with purity and simplicity of manners, the most enchanting graces that women can assume. The baneful effects of this dangerous poison, are visible in the countenances of those who make use of it, by their haggard looks and premature old age.
MR. HARCOURT. Lead is used in paintings with oil, not only as a colour, but as a dryer. It is likewise serviceable in assisting the melting of enamels and porcelain, and is the general basis of the glazing of pottery wares. The refiner finds it of great benefit in cleansing and assaying the noble metals.
HENRY. Lead seems to be a very useful metal. I know of several purposes to which it is applied.
MRS. HARCOURT. It is also subject to be abused, its poisonous quality rendering it highly dangerous to be taken internally, unless regulated by the judgment of a skilful physician. Avarice has occasionally induced some unprincipled persons to infuse salt of lead, which, from its sweetness, is called sugar of lead, into wine turned sour, with design to recover it. Lead is administered externally for wounds and ulcers; and Goulard's extract, so much approved for its efficacy in inflammation, is prepared by boiling and dissolving litharge, or the ash of lead, in vinegar. Now, Henry, favour us with what you have observed on the subject.
HENRY. Houses are covered with lead: gutter-pipes and cisterns are made of it; but I do not know how it is formed into sheets for these uses.
MRS. HARCOURT. Large blocks, called pigs of lead, furnished from the lead-works, are melted by the plumbers into shapes, by running the metal, when liquid, into moulds of brass, clay, or plaster. The lead intended for large sheets, to cover the roofs of houses and churches, is melted in a huge cauldron or furnace, and poured with ladles upon a table of extensive dimensions, covered with fine sand, and guarded with ledges. Pipes are sometimes cast; at others, they are made of a flat piece rolled round, and soldered together.
CHARLES. Lead is found in various countries, but it abounds particularly in England. Cornwall, Devonshire, and Somersetshire, yield a considerable quantity. Nor are our mines confined to the west: Derbyshire, Northumberland, and Durham, boast of some which are valuable. Wales, likewise, is very productive in this article. So poisonous is