Volume 1

The chemical works of Caspar Neumann ... / abridged and methodized. With large additions, containing the later discoveries and improvements made in chemistry and the arts depending thereon by William Lewis.

Caspar Neumann

Date:: 1773

Credit: The chemical works of Caspar Neumann ... / abridged and methodized. With large additions, containing the later discoveries and improvements made in chemistry and the arts depending thereon by William Lewis. Source: Wellcome Collection.

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$naces, and forms the bafis of the fine white cryftaL Flint. line kinds of Glafs, and of the compofitions for imita- ting precious (tones (c). Kunknel recommends the Sea- flints, as yielding a liner Glafs, and requiring lefs Salt, than thofe found onthe land : others objebt to the ma¬ rine Flints, that they make the Glafs brittle and apt to crack. Thofe which exhibit red veins when calcined, fhould either be reje£ted, or freed from that extraneous matter, which would give a tinge to the Glafs : this may be effected by walking the powder with Spirit of Vitriol or Aqua Regis, and afterwards edulcora¬ ting it with water. Such as have been pulverifed in an iron mortar fhould like wife be purified by the fame means from the ferrugineous particles they may have abraded from the inftrument, before they are em¬ ployed in the compofition of any curious Glafs. White Sand is often fufoftituted in the place of Flint, and does not confiderably differ from it in quality (d). Calces of Lead are commonly added, for the colourlefs as well as coloured glaffes, to promote the Vitrifica¬ tion. Though a moderate proportion of Ext Alcaline Diffolved Salt unites with Flint, in the fire, into a perfect glafs,in Aica- which is not diffoluble in any liquor, and difeoverslluSi B 3 no (c) Vitrification of Flint with other earths.] Powdered Flint lias been mixed in different proportions both with Quick-lime and with Earths of each of the other claffes, and urged with the mod intenfe fires procurable in the common furnaces, without Shewing any difpo- fition to melt: but thefe mixtures are brought into fuiion by a much lefs proportion of Salt than the ingredients fingly would require. Though Alcalies are the moft powerful flux for Flint by itfelr, Borax is found molt effectual ly to vitrify the compounds. (d) Sand.~\ Though the fine white Sands appear to the .eye to be purer than Flint, they fcarcely afford fo clear a glafs : the difference is the moft perceptible when each of them is melted with a fomewhat fmaller proportion of Alcali than is fufficient to bring them to their full trans¬ parency. Pott relates, that on melting Sand with half its weight of Nitre, he obtained a glafs of a purple colour j probably from fome me¬ tallic matter, of which moll Sands participate irt a greater or lefs de¬ gree. The red and yellow Sands are rnanifellly impregnated with a ferru- gineous calx. They contain alfo a minute portion of Gold \ which is feparable from them in the way of affay, though no method has hi¬ therto been found of extrafling it to advantage in the larger works. Cramer and others prefume, that there is no Sand in nature intirely free from Gold. Sez Gold.$