good substitute for black flux: it contains about 10 per cent of charcoal.

Argol, Cream of Tartar, Bi-tartrate of Potash.-When bi-tartrate of potash is heated in a covered crucible, a rapid decomposition takes place, accompanied by a disengagement of inflammable gases; the substance agglomerates, but without fusing or boiling up. The residue is black, blebby, and friable, and contains 15 per cent. of carbon when produced from rough tartar or argol, and 7 per cent. from cream of tartar.

These re-agents produce the same effects as black flux, and possess more reducing power, because they contain more combustible matter; but this is an inconvenience, because the excess prevents their entering into full fusion when the substance to be assayed requires but a small proportion of a reducing agent. They can be used with success in assays requiring much carbo

naceous matter.

Salt of Sorrel, Binoxalate of Potash, when heated is decomposed. It decrepitates feebly, and during its decomposition is covered with a blue flame; it at first softens, and when fully fused, is wholly converted into carbonate. When the oxalate is very pure, the resulting carbonate is perfectly white and free from charcoal; but very often it is spotted with blackish marks. It has no very great reducing power.

White, or Mottled Soap is a compound of soda with a fat acid. When heated in close vessels it fuses, boiling up considerably, and during its decomposition gives off smoke and combustible gases, and leaves a residue composed of carbonate of soda with about 5 per cent.

of charcoal. Of all reducing agents soap absorbs the greatest quantity of oxygen, and as the residue of its decomposition by heat affords but little charcoal, it has the property of forming very fluid slags. Nevertheless, it is rarely employed because certain inconveniencies outweigh its advantages. These inconveniencies are, its bubbling up and its extreme lightness. It also requires to be rasped, in order to mix it perfectly with the substances it is to decompose, and it then occupies a very large volume, and requires correspondingly large crucibles. There are nevertheless cases where it may be used with advantage by mixing it with other fluxes.

Reducing power of the various Fluxes.-By fusing each of the above-mentioned reducing fluxes with an excess of litharge, the same weight of each yielded the following quantities of lead:

By mixing rasped soap with binoxalate of potash or carbonate of soda excellent reducing fluxes may be made.

All those fluxes containing alkaline and carbonaceous substances are reducing and desulphurating, besides acting as fluxes, properly so called; they also produce another effect which it is useful to know, viz.: they have the property of introducing a certain quantity of potassium or sodium into the reduced metal. This was first pointed out by M. Vauquelin.* He found that when oxide of antimony, bismuth, or lead was fused with an excess of tartar, the metals obtained possessed some peculiar characters, which they owed to the presence of several per cents of potassium.

Metallic fluxes: Litharge and Ceruse.-These bodies always act as fluxes, but at the same time often produce an alloy with the metal contained in the ore to be assayed. Ceruse produces the same fluxing effect as litharge. The former is the better flux, and is very useful in a great number of assays.

Glass of Lead, Silicate of Lead.-The silicates of lead

* Annales des Mines.

are preferable to litharge in the treatment of substances containing no silica, or which contain earths or oxides not capable of forming a compound with oxide of lead, excepting by the aid of silica. It may be made by fusing 1 part of sand with 4 parts of litharge; if required more fusible, a larger proportion of litharge must be added.

Borates of Lead.-The borates of lead are better fluxes than the silicates when the substance to be assayed contains free earths; but in order to prevent them swelling up much when fused, they must contain an excess of oxide of lead. The borate of lead containing .9056 of oxide of lead and .0944 of boracic acid, is very good. Instead of borate of lead, a mixture of fused borax and litharge may be employed; it is equally serviceable.

Sulphate of Lead is decomposed by all siliceous matters and by lime, so that when these substances are present litharge is produced, which fluxes them.

Oxide of Copper is rarely used as a flux for oxidated matters, but is sometimes employed in the assays of gold and zinc to form an alloy with those metals. In this case a reducing flux must be mixed with the oxide. Metallic copper may be used, but is not so useful, as it cannot be so intimately mixed with the assay.

Oxides of Iron are good fluxes for the silicates. They are, however, rarely employed for that purpose; they are more often used to introduce metallic iron into an alloy to collect an infusible, or nearly infusible metal, by alloying it with iron, such as manganese, tungstenum, or molybdenum.

CHAPTER IV.

ON THE BLOW-PIPE AND ITS USEDISCRIMINATION OF MINERALS, &c.

NOTWITHSTANDING the able works already written on this portion of my subject, I should think the present deficient were I not to give a short account of the blow-pipe, its method of use, &c. I am the more inclined to do this, from the fact that the instrument to be presently considered is of much importance to the mineral analyst, (saving him, in some cases, days of needless labour); that these pages would not be that which they were intended, viz. a complete Guide to Practical Assaying, without giving short rules for its use. Having premised thus much, I hope my readers will excuse me carrying them over a path so well explored.

The blow-pipe formerly was only used by jewellers and workers of metal for producing sufficient heat for soldering certain small portions of their work; and it was only about the year 1738, that Anton Swab applied it to the analyses of mineral substances. Cronstedt used the blow-pipe to ascertain the difference between various mineral substances as to fusibility, &c. In 1765, Von Engestrom published Cronstedt's System of Mineralogy, and added to it a Treatise on the Blow