Anonymous

“ By Ignition is meant the exposure of a substance to such a degree of heat, that it glows or emits light, or becomes red-hot. Its greatest value is in the separation of a volatile substance from one less volatile, or one which is entirely fixed at the temperature of the flame. ”

“ A chemist can, with a blowpipe and a piece of charcoal, determine many substances without any reagents, thus enabling him, even when travelling, to make useful investigations with means which are always at his disposal. ”

“ In taking cognizance of water in relation to blowpipe analysis, we regard it only as existing in minerals. The examination for water is generally performed thus: the substance may be placed in a dry tube, and then submitted to heat over a spirit-lamp. If the water exists in the mineral mechanically it will soon be driven off, but if it exists chemically combined, the heat will fail to drive it off, or if it does, it will only partially effect it. The water will condense upon the cool portions of the tube, where it can be readily discerned. ”

“ ANTIMONY.—This metal fuses readily, and coats the charcoal under both flames with antimonious acid. This incrustation is of a white color where thick, but of a bluish tint where it is thin, and is found nearer to the assay than that of arsenic. When greatly heated by the flame of oxidation, it is driven from place to place without coloring the flame, but when volatilized by the flame of reduction, it tinges the flame blue. As antimonious acid is not so volatile as arsenious acid, they may thus be easily distinguished from one another. ”

“ The substance is thus deprived of a part, or the whole, of its oxygen, and becomes reduce according to the strength of the affinity which the substance itself has for oxygen. If the reduction of a substance is undertaken on platinum, by fusion with a flux, and if the oxide is difficult to reduce, the reduction will be completely effected only in the luminous part of the flame. But if a substance be reduced on charcoal, the reduction will take place in the blue part of the flame, as long as the access of air is cut off ”

“ The hydrate of strontia has the same properties as the hydrate of baryta, except that it is less soluble in water. The carbonate of strontia fuses a little at a red heat, swells, and bubbles up like cauliflower. This produces, in the blowpipe flame, an intense and splendid light, and now produces an alkaline reaction upon red litmus paper. The sulphate of strontia melts in the oxidation flame upon platinum foil, or upon charcoal, to a milk-white globule. This fuses upon charcoal, spreads and is reduced to the sulphide, which is absorbed by the charcoal. ”

“ Arsenic.—The arseniates and metallic arsenic itself impart to the blowpipe flame a fine blue color, provided that there is no other body present which may have a tendency to color the flame with its characteristic hue. The sublimate of arsenious acid which surrounds the assay, will give the same blue flame, when dissipated by the oxidation flame. The platinum forceps will answer for the exhibition of the color of arsenic, even though the salts be arseniates, whose bases possess the property of imparting their peculiar color to the flame, such as the arseniate of lime. ”

“ Many of the silicates give with borax a clear bead, while they form with microcosmic salt an opalescent one.
It frequently happens, that if a metallic oxide will not give its peculiar color in one of the flames, that it will in the other, as the difference in degree with which the metal is oxidized often determines the color. If the bead is heated in the reducing flame, it is well that it should be cooled rapidly to prevent a reoxidation. Reduction is much facilitated by the employment of metallic tin, whereby the protoxide or the reduced metal may be obtained in a comparatively brief time. ”

“ Microcosmic salt dissolves the oxides of iron in the oxidation flame to a clear bead, which, by the addition of a considerable quantity of iron, becomes of an orange color while hot, but gets lighter while cooling, presenting finally a greenish hue, and gradually becoming lighter, till, when cold, it is colorless. If the iron is increased, the hot bead presents a dark red color, but while cooling a brownish-red, which changes to a dirty-green, and, when cold, to a brownish-red color. ”

“ If the oxide of a metal is brought into the luminous portion of the flame produced as above, so that the flame envelopes the substance perfectly, the access of air is prevented. The partially consumed gases have now a strong affinity for oxygen, under the influence of the intense heat of that part of the flame. ”

“ If the current of air is blown too freely or violently into the flame, more air is forced there than is sufficient to consume the gases. This superfluous air only acts detrimentally, by cooling the flame.
In general the operation proceeds best when the substance is kept at a dull red heat. The blue cone must be kept free from straggling rays of the yellow or reduction flame. If the analysis be effected on charcoal, the blast should not be too strong, as a part of the coal would be converted into carbonic oxide, which would act antagonistically to the oxidation. ”

“ Cobalt (Co) occurs in combination with arsenic and sulphur, and associated with nickel and iron. It is found occasionally in combination with selenium, and there are a traces of it in meteoric iron. In the metallic state it is of a light, reddish-grey color, rather brittle, and only fusible at a strong white heat; at common temperatures it is unalterable by air or water. At a red heat, it oxidizes slowly and decomposes water; at a white heat it burns with a red flame. Cobalt is soluble in dilute sulphuric or hydrochloric acid by the aid of heat, whereby hydrogen is eliminated. ”

“ If certain reagents are mixed with many substances, changes are effected which would not ensue with heat alone. Formiate of soda possesses the property of readily reducing metallic oxides. When this salt is heated, it gives off a quantity of carbonic oxide gas. This gas, when in the presence of a metallic oxide, easily reduces the metal, by withdrawing its oxygen from it, and being changed into carbonic oxide. If a little fly-stone is mixed with some formiate of soda, and heated in the bulb, the arsenic is reduced, volatilized, and condenses in the cool portion of the tube. ”

“ There is nothing, perhaps, which will contribute more readily to the progress of the pupil, than thorough practice with the reactions recommended in this part of the work, for when once the student shall have acquired a practical eye in the discernment of the peculiar appearances of substances after they have undergone the decompositions produced by the strong heat of the blowpipe flame, together with the reactions incident to these changes, then he will have greatly progressed in his study, and the rest will be comparatively simple. ”

“ If the bead be heated on charcoal, a small tube or cavity must be scooped out of the charcoal, the bead placed in it, and the flame of reduction played upon it. When the bead is perfectly fused, it is taken up between the platinum forceps and pressed flat, so that the color may be the more readily discerned. This quick cooling also prevents the protoxides, if there be any present, from passing into a higher degree of oxidation. ”

“ Tellurium in the Metallic form.—By the aid of heat it is oxidized in sulphuric acid, a portion of the oxygen of the acid oxidizing the metal, while sulphurous acid gas escapes. This solution is colorless, and is tellurous acid, dissolved in sulphuric acid. It melts at a low red heat, and volatilizes at a higher temperature. If tellurium is heated with free access of air, it takes fire, and burns with a blue color, the flame being greenish at the edges, while a thick white vapor escapes, which has a feeble acidulous odor. ”