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acters. Where, in the above scale, two terms of comparison are employed, both must of course be attended to in the determination of the hardness.
Specific Gravity. This is also a character of great value in the determination of minerals. The specific gravity of a body is its weight compared with the weight of an equal bulk of pure water. In order to ascertain the specific gravity of a mineral we weigh the specimen first in air and then in water. The loss of weight in the latter case exactly equals the weight of the displaced water, or, in other words, of a volume of water equal to the volume of the mineral. Now, the specific gravity of pure water, at a temperature of about 620, being assumed to equal 1, or unity, it follows that the specific gravity of a mineral is obtained by dividing its weight in air by its loss of weight in water. Thus, if a = the weight in air, and w = the weight in water, G, or sp. gr. =
Example.- A piece of calcareous spar weighs 66 grs. in air, and 42 grs. when immersed in rain or distilled water. Hence its sp. gr.
66 66 42
The weight of the mineral may be ascertained most conveniently and with sufficient exactness for general purposes, by a pair of small scales such as are commonly called “apothecaries' scales.” These may be purchased for a couple of dollars, or even less. A small hole must be made in the centre of one of the pans for the passage of a horse-bair or silken fibre, about four inches in length, and furnished at its free end with a "slip-knot " or running noose, to hold the specimen whilst it is being weighed in water. The strings of the perforated pan may also be somewhat shortened, but the balance must in this case be brought into equilibrium by a few strokes of a file on the under side of the other pan, or by attaching thinner strings to it. If grain weights be used with this balance, the following will be required : 50 grs., 30, 20, 10, 5, 3, 2, 1, 0.5, 0.3, 0.2, 0.1.
The specific gravity bottle often recommended in mineralogical works, is too heavy to be carried by the scales described above. Bottles of the smallest capacity, weigh, when filled with water, at least 500 grains; and these scales will not carry more than 200, or 250 grains at the most. They are not very sensitive, indeed, when
This is the maximum specific gravity of calcareous spar.
loaded with more than 50 or 60 grains in each pan, although often of great delicacy when carrying lesser weights. The use of the sp. gr. bottle requires a chemical balance, costing, at the very lowest, some twenty-five or thirty dollars, besides being of difficult porta. bility; and hence its employment for general purposes is scarcely available.
Relative Malleability.-Some few minerals, as native gold, native silver, sulphide of silver, native copper, &c., are malleable or ductile, flattening out when struck, instead of breaking. A few other minerals, as talc, serpentine, &c., are sectile, or admit of being cut by a knife ; whilst the majority of minerals are brittle, or incapable of being cut or beaten out without breaking. In testing the relative malleability of a mineral, a s'n all fragment should be placed on a little anvil, or block of steel polished on one of its faces,* and struck once or twice by a light hammer. To prevent the fragment from flying off when struck, it may be covered by a strip of thin paper, held down by the forefinger and thumb of the left hand. Thus treated, malleable bodies flatten into discs or spangles, whilst brittle ones break into powder.
Magnetism.-Few minerals attract the magnet in their natural condition, although many do so after exposure to the blowpipe. (See below.) In trying if a mineral be magnetic, we chip off a small fragment, and apply to it a little horse-shoe magnet, such as may be purchased anywhere for a quarter of a dollar; or otherwise we apply the specimen to a properly suspended magnetic needle In this manner the black granular masses which occur frequently in our gneissoid or Laurentian rocks, and in the boulders derived from them, may easily be recognised as magnetic iron ore.f Many specimens of magnetic iron ore (and also of magnetic pyrites) exbibit “polarity,” or attract from a given point, one end of the needle, and repel the other.
Taste.—This is a very characteristic although limited property, being exhibited only by a few soluble minerals. In these, the taste may be saline, as in rock salt; or bitter, as in Epsom salt; or metal. lic, as in sulphate of iron, and so forth.
The little anvils called Watch-makers' anvils,' are very suitable for this purpose. They may be purchased (where Watch-makers' tools are sold) for half-a-dollar, or even less.
+ The other dark-coloured cleavable masses in these rocks consist of mica or more rarely of hornblende.
CHEMICAL CHARACTERS.*— These, so far as regards the determination of mineral species, comprise the results produced by the action of acids; and the relative fusibility, &c., of minerals, as ascertained by the employment of the blow-pipe.
Action of Acids.—The acid-test is resorted to, chiefly for the purpose of distinguishing the carbonates from other mineral substances. The majority of carbonates, as carbonate of lime, carbonate of oxide of copper, &c., when touched with a drop of diluted hydrochloric acid (the "spirit of salt " of the shops), produce a more or less vigorous effervescence. This reaction is still more marked, if a small fragment of the mineral be dropped into a test-tube containing a little of the acid. The effervescence arises from the escape of carbonic acid. Some carbonates, as carbonate of iron, dissolve very slowly, and scarcely produce any effervescence, unless employed in a pulverised state, or unless the acid be gently heated. Sulphate of lime and various other minerals dissolve in hydrochloric acid, but without causing effervescence. Quartz, feldspar, &c., on the other hand, are quite insoluble. Certain silicates, and more especially those named “ zeolites” dissolve partially in hot hydrochloric acid, leaving the undissolved silica in the form of a gelatinous mass. Gold and platinum are not attacked by strong nitric acid, which dissolves copper, silver, &c., very readily. Cupreous acid-solutions have always a green or blue colour. Red copper ore dissolves with effervescence in nitric acid producing a coloured solution; by which characters it may be readily distinguished from the red silver ores.
• The Chemical Characters of minerals are discussed in the present paper in the briefest terms. To have entered fully into these characters, would have carried us altogether beyond the object in view : the simple determination of the names of Canadian minerals. The advanced lectures given daily during the Michaelmas Term in University College, To ronto, by the author, are open to all students desirous of obtaining more ample information on the subject. The annexed extract is taken from the author's syllabus to this course of lectures:
"THE CHEMICAL RELATIONS OF MINERALOGY. " The Chemical Constitution of Minerals.- 1, Chemical Nomenclature as applied to Mineralogy ; 2, The Laws of Combination : 3, The Atomic Theory: 4, Chemical Notation : 5, Construction of Chemical Formulæ ; 6, Isomorphism, or Law of Substitution; 7, Atomic Volumes.
"The Chemical Eramination of Minerals.-1, Action of Acids, &c. 2, Employment of the Blow.pipe, comprising : a, Instruments and Appliances; 6. Reagents; c, Operations; d, Reactions; and e, Plan of analysis in the examination of an unknown substance."
Students atteuding these lectures, are strongly advised to go through, also, a course of Practical Chemistry, in the Laboratory of University College, under the direction of Profes. sor Croft.
The acids used in these experiments may be conveniently kept in small glass bottles furnished with a long glass stopper, reaching to the bottom of the bottle, and with a glass cap to prevent the escape
of corrosive fumes. For geological purposes (testing calcareous rocks, &c.,) strong hydrochloric acid diluted with half its bulk of pure water, is principally used. The “specimen basket” may be provided near its upper edge with a little nest, or wicker-work pocket, for the reception of the acid bottle.
Action of the Blow-pipe.-The blow-pipe in its simplest form is merely a narrow tube of brass or other metal, bent round at one extremity, and terminating at that end in a point with a very fine orifice (a: fig. 21). If we place the pointed end of this instrument
just within the flame (and a little above the wick) of a lamp or common candle, and then blow gently down the tube, the flame will be deflected into a horizontal position, and its heating powers will be wonderfully increased. Many minerals when held in the form of a thin splinter at the point of the blow-pipe flame, melt
with the greatest ease; and some are either wholly or partially volatilized. Other minerals, on the contrary, remain unaltered; and thus, by the aid of the blow-pipe, we are often enabled to distinguish from one another, in a moment, various minerals which in external characters may be closely alike.*
The blow. pipe has, strictly, a three-fold application. It may be employed, as just pointed out, to distinguish minerals from one another; some of these being fusible, whilst others are infusible ; some attracting the magnet after exposure to the blow-pipe, whilst others do not exhibit that reaction; some imparting a colour to the flame, others volatilizing, and so forth. Secondly, the blow-pipe may be employed to ascertain the general composition of a mineral, or the presence or absence of some particular substance in it, as copper, lead, iron, cobalt, manganese, sulphur, arsenic, and the like. Thirdly, the blow-pipe may be used to determine in certain special
. More convenient forms of blow-pipe will be found described in special works on the use of that instrument, but the common form described above is quite sufficient for the simple experiments required in the determination of our ordinary minerals.
cases the actual amount of a metallic or other ingredient previously ascertained to be present in the substance under examination.*
In the employment of the blow-pipe (in conjunction with external characters) in the simple determination of our Canadian minerals, we are never compelled to resort to more than two experiments: the fusion-trial, and the water-test. The student will find it of advantage, however, to study in addition the reactions of the more common metals and metallic oxides as given in special works on the Blowpipe. To describe these reactions in the present essay would extend the subject much beyond its allotted limits.
The Trial of Fusibility. In order to ascertain the relative fusibility of a substance, we chip off a small particle (the smaller the better) and expose the point of this to the extremity of the blow-pipe flame -holding the test-fragment in a small pair of tongs or forceps with platinum tips ;t or supporting it, if it be of a metallic aspect or of a certain weight and exhibit at the same time a coloured streak, on a piece of well-burnt pine charcoal. The particle thus exposed to the flame ought not to be larger than a small carraway seed. If it be fusible, its point, in the course of ten or fifteen seconds, will become rounded into a bead or globule. The proper method of blowing can be acquired by half-an-hour's practice. The cheeks are to be filled with air, and this is to be urged gently and continuously down the tube by the compression of the cheek muscles, the operator breathing at the same time (if he require to do so) through his nose. By a little practice this becomes exceedingly easy ; and the blowing need never be kept up (at least in experiments of this kind) for more than 3 quarter of a minute at a time. A thin splinter will exhibit signs of fusion in ten or twelve seconds, or not at all. The use of the instrument, therefore, is easily acquired, and is in no way injurious to the health. Thus treated :
(a) The test-fragment may decrepitate” or fly to pieces. Example, most specimens of galena. In this case, a larger fragment
. See, for example, a paper by the author “on the Assaying of Coals by the Blow-pipe," first published in this Journal: Vol. III., page 208. Also Plattner's " Probirkunst mit dem Lothröhre."
+ These forceps may be obtained from any dealer in chemical apparatus. For simple experiments they may be replaced by a strip of thin sheet ircn bent into the form of a pair of nippers or tongs. Some twine or silk must be twisted round the middle part to prevent the fingers from being burned. VOL. V.