With respect to the quantity of the substance which should be assayed when seeking its behaviour alone with the reagents before the Blowpipe, it is always advisable that too much be not taken. If, for instance, an analyst wishes to examine the solubility of an earth, mineral, et cetera, with borax or microcosmic salt, on the platinum wire, a piece about the size of a mustard seed is employed. In cases where metallic oxides are present, and the color only of the bead or glass is sought, considerably more is used, and in a pulverized state; but if it is the reduction of a metal by means of carbonate of soda upon charcoal, a still larger quantity is taken, and also in a powdered state. Experience, however, soon teaches the proper proportions in the different cases occurring. If too much substance be employed, it inevitably follows that uncertain results are the con

sequence.

In examining the relation of a substance by itself, or with fluxes before the Blowpipe, the operator proceeds as follows:

a. A part of the substance to be examined is gradually heated to redness, in a small glass retort, over the spirit lamp. During this process, all phenomena must be observed,-if decrepitation takes place, if water or any other volatile body be eliminated, and its odor. The water condensed in the cooler parts of the retort should be tested by litmus or Brazil wood paper, to ascertain if it gives an acid or an alkaline reaction.

B. Another portion is heated gently upon charcoal; the odor will indicate volatilized acids, arsenic, selenium, or sulphur. The difference of smell should be noticed, when the sample is heated in the oxidating as well as in the reducing flame, since selenium and sulphur are best detected in the former, and arsenic in the latter. It should be noticed if the charcoal has become coated with a sublimate, and if near or at a distance from the assay; of what color it is, and if it remains the same when cold as when hot. If the substance under examination be an earth, it must be heated strongly for some time, and then removed from the

charcoal to litmus paper, and moistened with a few drops of distilled water; if an alkaline reaction occurs, the substance contains a carbonate of one of the alkalies; for these occur in nature, Witherite, Strontianite, Calcareous spar. Magnesite, Bitter-spar, et cetera,-and become caustic with strong, heating, and exhibit alkaline properties.

γ.

If the mineral contains volatile metals, metallic oxides, sulphur, et cetera, it is examined in a tube which is open at both ends. The substance is placed within the tube, at a short distance from one end, which is then heated with the spirit-lamp, and afterwards with the Blowpipe flame. The tube is held in an inclined position. The more perpendicular the position, the stronger the current of air. It is very easy to regulate the rapidity of the draught according to the rate of oxidation that may be required.

In this treatment, many substances are sublimed, which were not when heated in the retort, because the access of air was comparatively small. The oxygen of the air is absorbed, forming volatile acids or metallic oxides; some escape as gases, and may easily be recognized by their smell,-sulphur, for instance, exhaling sulphurous acid. Others are deposited in the upper and cooler parts of the tube, at greater or less distances from the heated body, according to their degrees of volatility; in the cases of arsenic and antimony, for example, the former is given off as arsenious acid, and the latter as oxide of antimony.

8. In examining a substance with regard to its fusibility, a part is placed in a small cavity, formed in a piece of charcoal, and heated for a length of time in a strong oxidating flame. The more easily reduced metals and metallic oxides are acted upon in this experiment.

If the substance be an earth or silicate, small pieces of it are broken off with a hammer, and a fragment chosen with a sharp point or side. This is held between the platinum points of a pair of forceps, and a strong Blowpipe flame allowed to play on the sharp extremity for some time. It will at once be seen if the

substance is fusible. If infusible, the sharp point or edge will remain unaltered; if fusible, it becomes rounded; and if entirely fusible, it will melt into a round bead. These appearances should be examined through a strong magnifying glass. When a substance is heated in the inner flame, the outer may become colored; for instance, if the mineral contains potassa, the outer flame will be violet; if soda be present, the flame appears yellow; whilst lithia communicates a red tinge. If the three are together, the yellow flame predominates.

BERZELIUS treated those minerals which were found to be very infusible, in the following manner :-The substance is levigated in an agate mortar, with water. The menstruum, with the finely divided particles floating through it, is dropped on the charcoal, and heated by the oxidating flame, to evaporate the water. This operation is repeated until the charcoal becomes covered with a coating of the fine particles, which are carefully collected and held in the points of the forceps, and then subjected to a powerful oxidating flame. For the most part, some change takes place, owing to the extreme divisibility of the mineral, showing that the substance is not altogether infusible. In this case, the microscope will be in great requisition, in order to discern the action which may have been produced.

When a mineral occurs in a granulated state, such as sand, one of the grains should be placed on the charcoal; but as this is so apt to be lost, the better way is to knead the substance with water into a paste, which is then placed on the charcoal, dried by the oxidating flame, and examined as to its fusibility. This process should always be resorted to, when treating substances that are in a minute state of division.

The heat obtained by blowing through the small hand Blowpipe is limited, so that there are some bodies which are never fused before it; silica and alumina, for instance, in however finely divided a state. Many minerals melt and tumefy, and thereby give a blistered glass, which, on account of the air-bubbles, appear opaque. The intumescence and blistering appear at a certain degree of heat, that is, when all the water is expelled. According to BERZELIUS, the cauliflower appearance which some

F

times takes place on heating, proceeds from a change in the combination of the ingredients and their relative positions; but the tumefaction and blistering which occur in igneous fusion, he considers to arise only from the escape of some ingredients in the form of a gas, although it often happens that this ingredient is not discriminated in an analysis of the body. This occurs for the most part with silicate of lime or alkalies in combination with alumina.

The examination of the comparative fusibility of minerals is of essential importance, as many which consist principally of earths, and contain very little of the true metallic oxides, can readily be distinguished by this means. Hence it is that the list given by ROSE, in all the editions of his Manual of Analytical Chemistry, of a considerable number of minerals arranged according to their different degrees of fusibility, is of great interest.

Of the minerals which occur most frequently, the following are, when heated between the platinum points of a forceps in a strong flame, perfectly infusible :-Quartz, Corundum, Spinel, Zeylanite -Pleonaste-Automolite-Gahnite-Olivine, Cerite, Zircon, Disthène-Cyanite Leucite, Talc, Gehlenite, Anthophyllite, Staurolite, Allophane, Kymophane, Gadolinite. Those that phosphoresce on being heated:-Rutile Titaneisen-or Titaniferous Oxydulated Iron-Tantalite, Turquoise-Calaite-Chondrodite, Topaz. Very difficultly or only on the edges fusible, are particularly the following:-Adularite, Tetartine — Albite— Petalite, Labradorite, Anorthite, Tabular Spar, Meerschaum, Speckstein, Serpentine, Epidote. Those which tumefy on the first application of heat :-Dichroite-some varieties moderately fusible-Beryl-Emerald-Euclase, Titanite, Sodalite, Schwerstein-Tungstate of Lime-Heary Spar-Sulphate of Baryta— Celestine, Gypsum-Sulphate of Lime-Apatite, Fluorspar. The fusible are the Zeolites, the most of which present intumescence when heat is first applied, Oligoklas-Soda Spodumene -Spodumene, which also tumefies, Meionite, Elaolite, Nepheline, Amphibolite, the greater part of which effervesce during fusion. The Pyroxenes, of which those containing large quantities of magnesia are with difficulty fusible, Vesuvian, Idocrase, which

tumefies on melting, Orthite, which boils while fusing, Wolfram, Boracite, Datholite, Botryolite, Tourmaline, and Axinite, which swell up when melted, Amblygonite, Lazurstein, Hauyn, Nosin, Eudyalite, and Pyrosmalite.

e. The comportment of the substances with fluxes should be examined. The fluxes are BORAX, MICROCOSMIC SALT, and CARBONATE OF SODA.

§ 1.-TREATMENT OF THE SUBSTANCE WITH BORAX.

This can be performed either on a platinum wire or on charcoal. If the substance contains only earths and metallic oxides, it should be first examined on the wire. The following is the method of procedure: the loop of the platinum wire is first heated to redness in the Blowpipe flame, then rapidly dipped into the borax, and the adhering particles fused in the oxidating flame. As it seldom happens that a sufficient quantity of borax adheres the first time, the process should be repeated once or twice, until a bead is formed large enough to fill the loop completely. The bead generally remains so firmly fixed in the loop, that it cannot be removed without force. If the wire is quite clean, the bead will be perfectly colorless, both when hot and cold; if it should happen to be slightly tinged, which is easily perceived by holding it between the eye and the light, it must be removed from the platinum wire. The separation of the glass bead from the wire is easily effected, by heating the bead strongly, and then quickly removing it from the flame, placing it over a porcelain basin, and striking the wire against the rim; it immediately falls into the basin and solidifies. The quicker this operation is performed, and the firmer the wire is held, the more perfectly is the separation of the bead effected.

The borax bead melted on the platinum loop, must, when cold, be moistened on one side with the tongue, which side should then be brought in contact with the substance to be tested, in the state of fine grains, or of very fine powder, and the adhering particles melted, together with the borax, in the oxidating flame. In