A Practical Treatise on the Use of the Blowpipe, in Chemical and Mineral Analysis: Including a Systematic Arrangement of Simple Minerals, Adapted to Aid the Student in His Progress in Mineralogy, by Facilitating the Discovery of the Names of Species

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R. Griffin & Company, 1827 - Blowpipe - 308 pages
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Page 36 - The operation depends upon a little artifice in blowing through the pipe, which is in reality more difficult to describe than to acquire. " The effect intended to be produced is a continual stream of air for many minutes, if necessary, without ceasing. This is done by applying the tongue to the roof of the mouth, so as to interrupt the communication between the mouth and the passage of the nostrils ; by which means the operator is at liberty to breathe through the nostrils, at the same time that...
Page 108 - If you take two pieces of lead-foil •and platinum-foil of equal dimensions, and roll them together, and place the roll upon charcoal, and direct the flame of a. candle cautiously towards the edges of the roll, at about a red heat, the two metals will combine with a sort of explosive force, scattering their melted particles off the charcoal, and emitting light and heat in a very surprising manner. Then there will...
Page 4 - Lond., 1788. philosophical pursuits with the help of an assistant. He accordingly employed Assessor Gahn, who performed, under his directions, a series of operations on all the minerals then known, by which he was taught in what manner each individual conducted itself before the Blowpipe. The experience thus acquired enabled Gahn to employ the instrument in every kind of chemical and mineralogical inquiry; and he attained such a degree of skill in its use, that he could detect the presence of substances...
Page 37 - ... cavity of the mouth : all subsequent supplies of air are to be introduced in the same manner as the first. Thus, with a little practice, the power may be obtained of keeping up a continued blast for as many minutes as may be necessary for any ordinary operation.* IV.
Page 104 - If the quantity of oxide is so small that the green colour is not perceptible, its presence may be detected by the addition of a little tin, which occasions a reduction of the oxide to protoxide, and produces an opaque, red glass. If the oxide has been fused with borax, this colour is longer preserved ; but if with microcosmic salt, it soon disappears by a continuance of heat. The copper may also be precipitated upon iron, but the glass must be first saturated with iron.
Page 25 - Care must be taken that the stream of air does not strike against any part of the wick, as it would then be disturbed and split into several parts.
Page 44 - ... hole the substance to be examined must be put. The assay should be placed on the side of the charcoal, and not the end ; otherwise, the substance to be fused spreads about, and a round bead will not be formed. But Berzelius, in the following passage, gives us directions quite contrary (p. 31): — " In order to fix the flux to a point on the surface of the support, one of the ends perpendicular to the layers of the wood is to be chosen for its receptacle ; if placed on the section parallel to...
Page 105 - Alkalies or lime promote this precipitation. If the glass containing copper be exposed to a smoky flame, the copper is superficially reduced, and the glass covered while hot with an iridescent pellicle, which is not always permanent after cooling. It is very easily reduced by soda. Salts of copper, when heated before the blow-pipe, give a fine green flame. Oxide of Mercury before the blow-pipe becomes black, and is entirely volatilized.
Page 198 - Not affected by the mineral acids. When fused with carbonate of potash, and diluted with water, a white powder precipitates, heavier than the one employed. Before the blow-pipe it does not melt, but becomes opaque and brown. With microcosmic salt it forms a globule of glass, which appears black ; but its fragments are violet. With borax it forms a deep vellow glass with a tint of brown; with soda it divides and mixes, but does not form a transparent glass.
Page 10 - Children. form water, one essential character, the fusibility or iafusibility of different substances as determined by the common blow-pipe, disappears before the intense heat produced by this, which levels all bodies to one general class of fusible substances ; though very evident differences are still observable in the facility with which different bodies are reduced to the state of fusion. In return too for the character which is thus lost, we gain a new one in the appearance of the otherwise...

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