Talc

“ The masses of talc commonly sell for about a rupee and a half, or even up to two rupees per seer (of about two pounds avoirdupoise) : when good, it is of a pure pearl color, but it has, ordinarily, either a yellowish, or a faint blue cast: by means of proper tools, this mineral may be split into very thin leaves, which often present smooth surfaces, but are apt to have little scaly blisters, that greatly deteriorate their value. However, a seer of talc, that splits well, will sometimes yield a dozen or more panes, of about 4812 inches by 9, or of 10 by 10 ”

“ By the action of heat the hardness of the mineral is greatly increased. Pseudomorphs are known after actinolite, pyroxene, &c., and the mineral has probably been generally formed by the alteration of ferro-magnesian silicates. Talc occurs chiefly in crystalline schists, usually associated with chlorite, serpentine and dolomite. Fine examples of apple-green colour are found at Mount Greiner, in the Zillerthal, Tirol. Talc-schist is a foliated rock composed chiefly of tale, generally associated with quartz and felspar ”

“ By mixing 100 parts of prepared talc, while still moist, with 12 parts of spermaceti, previously rubbed to a moist powder with some rectified alcohol, and drying at a moderate heat, a product known in commerce as "Blanc fard," or "Blanc français," is obtained.
Talc by itself not furnishing a beautiful white, it is mixed, according to circumstances, with subnitrate of [Pg 336] bismuth (flake-white) , magnesia, chalk or zinc-white. White lead, though frequently used, cannot be recommended, it being injurious to health. Subnitrate of bismuth furnishes the best white ”

“ These minerals, arbitrarily selected for standards, are successively harder from talc the softest, to diamond the hardest of all minerals: a piece of talc is readily scratched by gypsum, and so on throughout the scale. A mineral which is capable of scratching calcite and itself be as easily scratched by fluor-spar is said to have a hardness of 31/2. Some care is required to avoid error in the determination of hardness: it is best to select a smooth crystal-face, cleavage-surface or fracture on which to rub a sharp corner of the scratching mineral ”

“ Beautiful white talc, and small crystals of sulphuret of iron, are disseminated in the mass. Specimens of this mass are in almost all the cabinets in America. Smaller masses have been found associated with feldspar. Small crystals of this mineral are very common in mica slate, with staurotide and garnet. Two of these crystals are often arranged at right angles with each other. In Cornwall it is found in small crystals in the gneiss containing graphite. ”

“ Some become chloritic from the development of the soft, green hydrated mineral, chlorite, derived from the pyroxene, amphibole, biotite, and perhaps other silicates of the original rock. Others become talcose from the development of talc, a very soft, unctuous, hydrous magnesian silicate developed from the magnesian minerals of the original rock. Soapstone or steatite is a rock composed essentially of such secondary material. ”

“ The luster of the foliated varieties is apt to be pearly, and the color apple-green to white, though sometimes stained brown from oxide of iron. The streak of the mineral is white except when stained by iron. Although the rocks which are composed mainly of talc (soapstone) are exceedingly soft, they are very tough and remarkably resistant. Hardness 1-1.5. Specific gravity 2.7-2.8.
Serpentine.—Like talc, serpentine is a silicate of magnesium and hydroxyl, and an important product of the breaking down of magnesium minerals in the process of weathering. ”

“ Now, as nothing contributes more than health to the preserving of beauty, this has given occasion to the chemists to search this oil of talc, which is to maintain the body in this disposition, and to engage the ladies to be at the expense of the search. ”

“ It has been reckoned a species of talc by Justi, by Wallerius in the first edition of his mineralogy, and also by others. Its durability in resisting heat is certainly manifested, when it is kept in a close fire and between coals. But it is proved by the experiments of modern mineralogists, that in an open, strong, and long-continued fire, it becomes almost entirely consumed.
Bartholomew Ambrosinus, in the continuation of Aldrovandi’s Musæum Metallicum, printed at Bologna in 1648, uses the name lapis plumbarius. ”

“ Le talc est commun, surtout près de Larnaca, où on l’emploie à blanchir les maisons; et le plàtre a de nombreuses carrières.
The “talc” may be the same with the “Lapis specularis,” which was found in Cyprus, according to Pliny (xxxvi. 45.) . The testimony of Sonnini so far agrees with those of the ancients, that all the places mentioned were on the northern side of the island, so that the asbestos seems to have been found between Solæ towards the West and Carpas towards the East. ”

“ The connection of this substance with the Andalusite of Douce is remarkable; the latter often forming the nucleus of crystals externally of four sides, sometimes filling nearly the whole of the interior, but in other specimens, forming little more than an axis, with rounded edges, and of irregular form, from which the folia of the investing talc-like substance appear to radiate. ”

“ At Perranbonse Cove, near the church, the slate is a variety of schistose diallage rock, such as has been already described at Cadgwith.
Near the lighthouses the cliff is formed of a glossy decomposing talcose slate, which has been called by some geologists Micaceous schist, but talc appears to be the characteristic mineral, as it is present in a distinct form throughout the veins, with nodules of quartz abounding in this slate. ”

“ In some cases, also, talc results from the alteration of igneous rocks without mashing—as in the case of the large talc and soapstone deposits of Virginia, which are the result of rather complete alteration of basic igneous rocks such as peridotites and pyroxenites. ”

“ The lamellar and slaty varieties of common hornblende are very common.
Radiated actynolite of a beautiful bluish green in Litchfield; in Canton of a brownish green.
Steatite is common, and is quarried in Litchfield. The varieties of talc are very common, connected with steatite, cyanite, and chlorite.
Chlorite in Litchfield, is found on quartz, with talc.
Porcelain clay in Litchfield in small quantities, and in Washington.
Graphite is found in Cornwall in great quantities. Its gangue is gneiss and sienite. It is lamellar, and has a metallic lustre; is easily obtained, and might be made useful. ”

“ It would thence appear that the presence of talc is of no use towards the fusibility of the silica, and that its absence may be supplied by increasing the dose of the flux. In all cases, however, we ought to beware of metallic oxides in the sand, particularly those of iron and manganese, which most frequently occur, and always injure the whiteness of the frit.
The ancients carried the art of enamelling to a very high perfection, and we occasionally find beautiful specimens of their work, of which we know neither the composition, nor the manner of applying it. ”

“ Dose for children from 10 to 15 years, one half-tablet. From 5 to 10 years, one-quarter of a tablet. Below these years, the medicine should not be given.
[Pg 54] The average weight of the tablets was 11·2 grains; among 12 weighed separately the weights varied from 10·5 to 12·5 grains. Analysis showed the presence of potassium iodide, guaiacum resin, extract of liquorice, powdered liquorice, starch, mineral matter—apparently a mixture of talc and kaolin—a resinoid substance, and a trace of alkaloid. The alkaloid amounted to 0·016 per cent. ”

“ It is much more convenient for drawing than pen and ink, because the marks made with it appear distinct upon a white ground, also, in consequence of its brightness, show themselves on black, and can be preserved or rubbed out at pleasure. This mineral is smooth, appears greasy to the touch, and has a leaden-colour, which it communicates with a metallic brightness. It can resist, for a long time, the strongest fire, and even from it requires more hardness; it has, in consequence, been thought to be a species of talc. ”

“ The small tablets had an average weight of 34·3 grains. Analysis showed them to contain sodium bicarbonate and tartaric acid, but in this case [Pg 97] the latter was in excess and the product acid; the other ingredients were sodium chloride, phenolphthalein, and talc. The results of quantitative determinations indicated the following formula (more carbon dioxide had been lost in this case; the figures add up to 108·5, the reason being that given above) :
The estimated cost of the ingredients of the contents of a 2s. ”

“ Earthy minerals, including asbestos, barytes, clays, gypsum, infusorial earth, sandstone, marble, mica, phosphates, potash, rock salt, soda, sulphur, steatite, slate, talc, and all other substances of a like nature to any of them. ”

“ Babies have come to my clinic with cakes of talcum under their arms, and particularly between their thighs and in the crease of the buttocks. Here the well-meaning but thoughtless mother had reasoned, "a little is good; more is better" which is not always the case.
Talcum is not used to replace careful drying, and it should never be found in quantities on the baby's skin any more than you would expect to find quantities of face powder caked in the creases of the neck or behind the ears of an adult. ”

“ Such is the behaviour of Argillaceous earth; it admits besides of combining with water, that antetype of the salts.
3. The Inflammable earths must be soluble in acids and exhibit electric or aerial properties. Such is the behaviour of the Talcose earths; its minerals are unctuous, fall when exposed to the air into electric lamellæ, and burn brittle.
4. The Metallic earths must undergo change in acids, air and fire. The calcareous earth dissolves in all acids,107 burns corrosive and becomes almost a metallic calx. The Orders of earth are consequently ”

“ If we sprinkle thallium salt in the flame the green line of that element will be visible in the spectrum. If we take the lamp away and place a lime light or a piece of white-hot iron in front of the slit we shall get a brilliant continuous spectrum not crossed by any lines, either bright or dark. Insert now the alcohol-sodium-thallium lamp between the lime light and the slit, and the observer will see the two sodium lines and one thallium line in the same places as before, but as dark lines on a background of bright continuous spectrum, as: illustrated in the lower of the two spectra. ”

“ It melts at 720° and decomposes rapidly above 800°, giving oxygen and thallous oxide. Thallous chloride, TlCl, is readily obtained from the solution of any thallous salt, by the addition of hydrochloric acid, as a white precipitate similar in appearance to silver chloride, like which it turns violet in the light and fuses below redness into a (yellow) liquid which freezes into a horn-like flexible mass. It is also formed when the metal is burnt in chlorine. The specific gravity of this “horn” thallium is 7.02. ”

“ It is sometimes necessary to calculate the value of solutions according to the principles just explained, when several successive reactions are involved. Such problems may be solved by a series of proportions, but it is usually possible to eliminate the common factors and solve but a single one. For example, the amount of MnO_{2} in a sample of the mineral pyrolusite may be determined by dissolving the mineral in hydrochloric acid, absorbing the evolved chlorine in a solution of potassium iodide, and measuring the liberated iodine by titration with a standard solution of sodium thiosulphate. ”

“ Thallic oxide, Tl2O3, is obtained as a dark reddish powder, insoluble in water and alkalis, by plunging molten thallium into oxygen, or by electrolysing water, using a thallium anode. Thallic hydroxide, Tl (OH) 3, is obtained as a brown precipitate by adding a hot solution of thallous chloride in sodium carbonate to a solution of sodium hypochlorite. On drying it has the composition TlO (OH) . Hydrochloric acid gives thallous chloride and chlorine; sulphuric acid gives off oxygen ”

“ This idea was easily put to the test of experiment. A sheet of paper was moistened with a much weaker solution of salt than usual, and when dry, it was washed with nitrate of silver. This paper, when exposed to the sunshine, immediately manifested a far greater degree of sensitiveness than I had witnessed before, the whole of its surface turning black uniformly and rapidly: establishing at once and beyond all question the important fact, that a lesser quantity of salt produced a greater effect. ”

“ Polarised light is a very useful adjunct in the examination of starch granules. In the microscopical investigation, a minute portion of the sample is placed upon the glass slide and well moistened with a solution of 1 part glycerine in 2 parts of water; it is then protected by a thin glass cover, which is put on with gentle pressure. The appearance of various starches, under polarised light, is seen in Plate IX., where the cross lies at the hilum or nucleus of the granule and the form and relative size is visible in outline. ”

“ Thallium, as we shall afterwards see and as was observed on its discovery, has much kinship with lead and mercury, but some of its properties appertain to lithium and potassium. Naturally, where it is impossible to make measurements one is reluctantly obliged to limit oneself to approximate comparisons, founded on apparent signs which are not distinct and are wanting in exactitude. But in the elements there is one accurately measurable property, which is subject to no doubt—namely, that property which is expressed in their atomic weights. ”