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b. Nitrate of potassa also has the power of oxidizing arsenic and chromium; converting them into acids which combine with its base.

5. BISULPHATE OF POTASSA. KO, SO3, HO, SO3.

This compound generally presents itself when the neutral sulphate is strongly heated with oil of vitriol. If the bisulphate obtained contains too much acid, which must, if possible, be avoided, it emits thick white vapors, when heated only slightly. Bisulphate of potassa, in solution, indicates lithia, boracic acid, nitric acid, hydrofluoric acid, bromine, and iodine; and separates baryta and strontia from other earths and metallic oxides.

6. VITRIFIED BORACIC ACID. B3.

This acid is generally prepared by dissolving the borax in four times its weight of water, at 100° C; the solution is filtered while hot, and a quantity of oil of vitriol, equal to one-fourth of the weight of the borax, immediately added. The sulphuric acid unites with the soda, and forms sulphate of soda, which remains in solution; while the boracic acid, on cooling, separates in thin shining crystalline plates. These plates are drained, and being sparingly soluble, may be washed with cold water, and, afterwards, re-dissolved in boiling water, and re-crystallized. The boracic acid still retains a small quantity of sulphuric acid, probably in a state of chemical combination, and if required of absolute purity, must be fused at a red heat in a platinum crucible, then re-dissolved and crystallized. The density of the vitrified acid is 1.83. It serves, in qualitative examinations, to detect the presence of phosphoric acid in minerals, and small portions of copper in lead alloys. In quantitative analysis, it is generally used to ascertain the quantity of copper contained in a lead ore, and also the amount of copper united with various metals.

7. NITRATE OF COBALT IN SOLUTION.

The pure metal must be dissolved in dilute nitric acid, the solution evaporated to dryness, and the residue dissolved and filtered, to separate any foreign matter.

There are a few substances not easily distinguished by simple ignition, which acquire marked characters on being moistened with a solution of nitrate of cobalt, and then heated strongly in the oxidating flame. These are,

Alumina, acquiring a beautiful pale blue color,
Magnesia, a rose-red tint,

Zinc, a bright green, and
Tin, a bluish green.

A few drops of a solution of cobalt may be placed upon the substance by means of platinum wire, or a small pipette.

8. OXALATE OF NICKEL. NiO, Ō.

It is obtained perfectly pure in the following manner :-Heat copper-nickel-arsenic-nickel to redness with a quantity of borax in a clay crucible, and when in a state of fusion remove the crucible from the muffle, and expose it to a free current of air. If the ore had contained iron, cobalt, lead, antimony, or sulphur, they would have been oxidized and dissolved in the borax, while the nickel would remain in combination with the arsenic. Separate the nickel compound from the dross, and examine a portion of it before the Blowpipe for cobalt. If it be not free from this metal, repeat the preceding operation with borax. When the mixture is entirely free from cobalt, heat it strongly with a quantity of carbonate of soda and nitrate of potassa; during this process the arsenic acid combines with the soda or potassa, and the oxide of nickel remains in an uncombined state. Dissolve the soluble part of the residue in boiling water, and filter. The oxide of nickel which remains, after being well affused with water, must be dissolved in hydrochloric acid, with the aid of heat, and the nickel precipitated by oxalic acid.

If the arsenic-nickel should contain copper, it must be precipitated from an acid solution of it, by sulphide of hydrogen, previously to the heating with borax.

The oxalate of nickel is used in qualitative examinations for the detection of potassa, in a salt which also contains soda or lithia.

9. BLACK OXIDE OF COPPER. Cu O.

It may be obtained artificially, by calcining metallic copper; by precipitating it from the salts of copper with a solution of pure potassa; or by heating nitrate of copper to redness.

It is useful for ascertaining the presence of small quantities of chlorine, when in combination, et cetera.

10. SILICA, OR SILICIC ACID. Si Oo.

This compound is obtained in a state of purity as follows:Heat to redness in a platinum crucible, powdered rock crystal— quartz, with a quantity of carbonate of soda or potassa; dissolve the fused compound in water; add to the solution a quantity of hydrochloric acid, and evaporate to dryness. A fine gritty powder remains, which, being well affused with boiling water, and then ignited, gives pure silica.

Silica, with soda, is an excellent test for the presence of sulphuric acid; and, when in combination with borax or soda, separates tin from copper.

11. FLUOR SPAR. Ca F.

This salt must be freed from its water of crystallization. It serves, when mixed with bisulphate of potassa, to detect lithia, and boracic acid, in their various combinations. It is also a reagent for and is an excellent flux for ores. gypsum,

12. SULPHATE OF LIME. Ca O, SO3-Gypsum.

It must be kept for analysis in an anhydrous state. It is easily obtained free from water, by heating to redness a quantity of it, in a powdered state, in a platinum or porcelain crucible. It occurs abundantly in Derbyshire, Yorkshire, and Saxony; and in various forms. It can be prepared artificially, by adding sulphuric acid to any soluble salt of lime.

Anhydrous gypsum, in Blowpipe analysis, serves as a reagent for fluor spar. If small quantities of these two substances be placed slightly apart upon charcoal, and heated in the oxidating flame, both melt and run into each other, producing a colorless bead, which becomes opaque upon cooling. If an excess of gyp

sum is present, the bead will be colorless also. According to BERZELIUS, the clear glass appears to be a compound of hydrofluoric and sulphuric acids with lime, which, if exposed too long to the oxidating, or too short a time to the reducing flame, is decomposed, sulphurous acid being eliminated.

Sulphate of lime, sulphate of baryta, and sulphate of strontia fuse with fluor spar; also fluorides of barium and strontium, with gypsum, as well as with fluor spar.

13. BONE ASHES.

They are employed in the cupellation of gold and silver. HARKORT reduced them to many states of minute division by the processes of sifting and washing. The bones are burnt until they become perfectly white, and then freed from any carbonaceous matter that may have adhered to them. This being done, they are pulverized in a mortar, and the finer portions separated by a sieve. The remaining powder is then thrown upon a filter, and treated with boiling water, which extracts the soluble matter. The washing, which is then resorted to, is for procuring the boneashes of a more uniform degree of fineness. The mass from the filter is mixed with water in any cylindrical glass, allowed to settle for a few moments, and then decanted; the coarser powder is deposited at the bottom of the vessel, while the finer passes over suspended in the water. By repeated decantations in this. way, sediments are obtained of different degrees of fineness, the last, or that which remains longest floating through the liquid, being the finest. The resulting powders must be kept in separate phials. The coarser ashes are used for the cupellation of rich silver ores, and the finer, for assaying ores in which only a minute quantity of gold or silver is present.

14. PROOF LEAD. Pb.

It is employed either in a finely-divided state, or else in small fragments; but it must be entirely free from traces of gold, silver, or copper, as it is used in the quantitative analysis of these metals. The lead from the silver-smelting furnaces will answer both purposes, if properly sifted. If such lead is not easily ob

tained, the operator can prepare his proof lead in the following manner :-Dissolve acetate of lead in a small quantity of hot water, filter, and then add plates of zinc to the solution until the metallic lead is wholly deposited. Dry the resulting lead between folds of bibulous paper, and keep it at hand in a stoppered phial. When this lead is employed in silver and gold cupellations, it need not be accurately weighed, but quantities of it taken, to save time and trouble, according to the standard given in the lead measure, previously described at page 30.

The method just described is the best for obtaining lead perfectly pure, and in a minute state of division.

15. CHLORIDE OF SODIUM. NaCl.

It is taken either in a powdered or melted state; but its use is very limited. It is principally employed for glazing the earthen crucibles in which quantitative lead assays are performed.

16. CHARCOAL POWDER.

This can easily be obtained by triturating pieces of charcoal in a mortar. It is generally employed for roasting or smelting, in quantitative tin or lead examinations.

17. GRAPHITE-Plumbago.

It is used quantitatively, when free from impurities, for roasting earths, minerals, and various products, upon copper. When a good kind of graphite cannot be obtained, pure anthracite may be substituted. The graphite which is generally met with is so impure, that an operator, to get the best pieces, must pick from a mass of it those fragments which are unctuous to the touch, and in scales. These parts are then heated in a crucible, and afterwards well pulverized. If this graphite contains over ten per cent. of foreign matter, it must, previously to being used, be digested in nitro-hydrochloric acid to free it from iron and other impurities. Plumbago is extensively used for the manufacture of crucibles, as they are very durable, and sustain an intense heat. The composition of the plumbago of Cornwall is 960 carbon, and 4.0 iron.

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