Practical Electricity and Magnetism

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Longmans, Green, and Company, 1898 - Electric measurements - 388 pages

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Page 111 - As a unit of resistance, the international ohm, which is based upon the ohm equal to 10" units of resistance of the CGS system of electromagnetic units, and is represented by the resistance offered to an unvarying electric current by a column of mercury at the temperature of melting ice, 14.4521 grams in mass, of a constant cross-sectional area and of the length of 106.3 centimetres.
Page 173 - Prepare a neutral saturated solution of pure (" pure recrystallized ") zinc sulphate by mixing in a flask distilled water with nearly twice its weight of crystals of pure zinc sulphate, and adding zinc oxide in the proportion of about 2 per cent by weight of the zinc sulphate crystals to neutralize any free acid. The crystals should be dissolved with the aid of gentle heat, but the temperature to which the solution is raised should not exceed 30 C.
Page 172 - The volt, which has the value 10s, in terms of the centimetre, the gramme, and the second of time, being the electrical pressure that, if steadily applied to a conductor whose resistance is one ohm, will produce a current of one ampere, and which is represented by 0'6974 ({•) of the electrical pressure at a temperature of 15 C.
Page 174 - The glass tube containing the platinum wire should project some way above the top of the marine glue. The cell may be sealed in a more permanent manner by coating the marine glue, when it is set, with a solution of sodium silicate, and leaving it to harden. The cell thus set up may be mounted in any desirable manner. It is convenient to arrange the mounting so that the cell may be immersed in a water bath up to the level of, say, the upper surface of the cork.
Page 150 - Care must be taken that the clock used is keeping correct time during this interval. The solution is now removed from the bowl and the deposit is washed with distilled water and left to soak for at least six hours. It is then...
Page 150 - C. After cooling in a desiccator it is weighed again. The gain in weight gives the silver deposited. To find the current in amperes, this...
Page 150 - The anode is then immersed in the solution so as to be well covered by it, and supported in that position ; the connections to the rest of the circuit are made.
Page 175 - It is convenient to arrange the mounting so that the cell may be immersed in a water bath up to the level of, say, the upper surface of the cork. Its temperature can then be determined more accurately than is possible when the cell is in air. In luing the cell sudden variations of temperature should as far as possible lie avoided.
Page 174 - The ends of the wire project from the ends of the tube ; one end forms the terminal, the other end and a portion of the glass tube dip into the mercury. Clean the glass tube and platinum wire carefully, then heat the exposed end of the platinum red hot and insert it in the mercury in the test-tube, taking care that the whole of the exposed platinum is covered.
Page 173 - Keep the paste for an hour at this temperature, agitating it from time to time, then allow it to cool ; continue to shake it occasionally while it is cooling. Crystals of zinc sulphate should then be distinctly visible, and should be distributed throughout the mass.

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