Chemical and Pharmaceutic Manipulations: A Manual of the Mechanical and Chemico-mechanical Operations of the Laboratory ... For the Use of Chemists, Druggists, Teachers and Students

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Lindsay and Blakiston, 1849 - 482 pages
 

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Page 187 - ... will prevent the metal from running away, and in a few minutes it will cool and take the impression, without the slightest injury to the paper from which it was taken.
Page 281 - ... a warm situation, over the sand-bath or near the ash-pit, or in the sun's rays. They should not be allowed to dry rapidly or irregularly, and should be moved now and then to change their positions. To prevent cracking during desiccation, and the consequent separation of the coat from the vessel, some chemists recommend the introduction of fibrous substances into the lute, so as mechanically to increase the tenacity of its parts. Horse-dung, chopped hay and straw, horse- and cow-hair, and tow...
Page 273 - ... of the tube, and close the stop-cock. The air in the short leg is now of the same elasticity as that of the atmosphere at the spot ; and the air at the surface of the earth is under the pressure due to the weight of its own superincumbent mass. The amount of this pressure is ascertained by observing the height of the mercurial column in the barometer at the time. Next, pour mercury into the open and longer limb of the bent tube ; the air in the shorter limb will slowly diminish in bulk. When...
Page 137 - When such an arrangement is exposed to a high temperature, it is obvious that the expansion of the metallic bar will force the index forward to the amount of the excess of its expansion over that of the black-lead, and that, when again cooled, it will be left at the point of greatest elongation.
Page 279 - Iron cement. This mixture is used for making permanent joints generally between surfaces of iron. Clean iron borings, or turnings, are to be slightly pounded, so as to be broken but not pulverized ; the result is to be sifted coarsely, mixed with powdered sal ammoniac and sulphur, and enough water to moisten the whole slightly. It is then to be rammed or caulked into the joints, and the latter drawn together as tightly as possible.
Page 94 - A piece of wire, four inches long, on which a screw is cut, proceeds from the middle of the beam downwards. This is pointed to serve as an index, and a small brass ball moves on the screw, by changing the situation of which the place of the centre of gravity may be varied at pleasure. The fulcrum, as before remarked, rests upon an agate plane throughout its whole length, and the scale-pans are attached to planes of agate which rest upon the knife-edges forming the points of support. This method of...
Page 281 - ... adding the latter to effect the mixture, at first by stirring up the mass lightly with a pointed stick or fork ; it will then be found easy, by a little management, to obtain a good mixture without making it very moist.
Page 137 - ... with it, which moves upon the face of the arc, and subdivides the former graduation into minutes of a degree ; the other end crosses the centre, and terminates in an obtuse steel point, turned inwards at a right angle.
Page 226 - The cupel containing the lead of the alloy is then placed upon the sand and immediately covered by the crucible, taking care that the notch in its side shall be opposite to, and correspond with, the furnace door; more fuel is added, during which it is well to cover the hole in the top of the muffle with a crucible lid in order to prevent the admission of dirt. When the muffle has become throughout of a bright red heat the furnace door is thrown open...
Page 191 - Mixtures, having the power of generating or creating cold, without the aid of ice, sufficient for all useful and philosophical purposes, in any part of the world at any season.

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