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the want of all the above properties & by its property of becoming a white powder like plaster of Paris, by Calcination with a moderate fire, which powder mixed with water, suddenly dries & hardens without evaporation of the water. In the same manner the distinguishing marks of the other Classes of earth, as the talks, asbestus, &c, &c, and of other mineral substances as metals ought to be remembered and are found in Cronstedt. The sections therefore in that Book which treat of these ought chiefly to be attended to, & the rest may be passed over till there is an occasion of consulting them or may be read afterwards. These Sections are 1, 2, 3, 4, 13, 40, 68, 77, 93, 97, 102, 108, 113, 119, 120, 135, 144, 163, 164, 167, 179, 184, 192, 201, 216,221, 227, 232, 238, 246, 254, 260, 261, 271, 280, 294.
3. It is very difficult & requires much experience to know the contents of an Ore from its external appearance or even from descriptions of Authors. They must therefore be essayed either by acid menstruums or by reduction with fluxes in a Crucible with a melting heat. These methods are treated in Cramer's Book. Here also the distinguishing marks of the several metals as they are delivered by Cramer but more methodically in the Sections above mentioned ought to be attended to. Some of these afford easy methods of discovering the contents of Ores. Thus if an Ore be suspected to contain Iron, let it be powdered & calcined together with some Charcoal dust, or flower so as to be made red hot and when cold, apply a Magnet, or add some aqua regia & after it has stood a while, drop a little of this Solution into an infusion of [indecipherable], by which it will be turned black like ink. When into a solution of Gold in Aqua regia diluted with water a few drops of solution of tin is added a beautiful purple powder or precipitate is produced and thus Gold may be discovered.
Copper may be discovered by adding a few drops of Spirit of Sal amoniac to a solution of the Ore previously powdered and calcined in Aqua regia by which means the solution will soon become of a blue Colour. Regulus of Cobalt may be known by the calcined ore being fused with Borax and forming a blue Glass. Silver or Lead may be known by dissolving some of the calcined ore in pure spirit of nitre & adding a few drops of spirit of Salt by which these metals will become a white powder & will fall down. Zinc may be known by cementing the ore with Copper and forming brass in the manner directed by Cramer. Arsenic by the smell & whitening of Copper. To obtain the metal in substance that the quantity may be ascertained, the following method is in my opinion preferable to any described by Cramer or other author and may serve for all ores excepting of the volatile metals, as Zinc.
Let a quantity suppose two ounces of the Ore be powdered small & calcined in an open vessell or rather upon a flatt earthen or iron plate, till it no longer has any disagreeable smell. For this purpose let it be kept red hot. Take an ounce of this, an ounce & a half of glass of Borax, a quarter of an ounce of wheat flower, mix them very well, put them in a Crucible, press them down, fill the Crucible with Sea Salt, put this Crucible in another Crucible a size larger, set them in a melting furnace, or upon a Smith's forge or in a Chamber fire, surrounded well with Coals and raise the heat by Bellows, keep it thus melted during half an Hour, take the Crucible out of the fire, when cold break it, and you will find at the bottom the piece of metal. The heat must be encreased or diminished acording to the nature of the Ore as some require more heat & some less. The use of the two Crucibles is to prevent the loss of the metal if the Borax should dissolve the first Crucible and so pass through it, an inconvenience this method is liable to, to prevent which when a great heat is required, about a quarter of an Ounce of Sand ought to be added to the mixture that is to be put into the Crucible.
The Crucible ought to be large enough to hold twice the quantity of mixture & the rest of the space to be filled with Sea Salt. For the method of making glass of Borax, see Cramer. It is very easy. Small quantities of Ore may be essayed thus in a [clay] Tobacco pipe or small Crucible in a Chamber fire taking care to keep the tobacco pipe or Crucible surrounded with hot coals, & blowing with one or two pairs of bellows directly against it, through three inches of live coals. The mouth of the tobacco pipe or Crucible may be filled with wet clay to prevent dirt, coals, or ashes from falling in, and when it is thus surrounded & covered by Coals, ashes or small wet coals may be thrown upon the fire to keep in the heat, excited by the blast. By this means a very intense heat may be applyed to a small quantity of substance in a common grate, sufficient to essay any Ore, or try the fusibility of almost any earth. The tobacco pipe is convenient because its shank rests upon the barrs of the Grate & does not sink. If a Crucible be used, it ought to be placed upon a piece of brick to prevent it sinking. The blow pipe is also exceedingly convenient to those that can use it well.