A Handbook of Electrical Testing

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E. & F.N. Spon, 1887 - Electric measurements - 551 pages
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Page 143 - S04) can be obtained commercially ;* but it may be prepared by dissolving pure mercury in excess in hot sulphuric acid at a temperature below the boilingpoint ; the salt, which is a nearly insoluble white powder, should be well washed in distilled water, and care should be taken to obtain it free from the mercuric sulphate (persulphate), the presence of which may be known by the mixture turning yellowish on the addition of water. The careful washing of the salt is a matter of essential importance,...
Page 480 - The total resistance of a parallel circuit is equal to the reciprocal of the sum of the reciprocals of the individual resistances of the circuit.
Page 64 - A small mirror of i metre focus is affixed to the suspended coil ; a brass spring at the bottom keeps the suspending wires adequately stretched ; and a screwhead at the top of the instrument serves both to regulate the tension in the wires and to let the coil down, to a position of rest on the central iron cylinder, whenever the galvanometer is to be dismounted for removal to a distant place. The resistance of the coil is about 150 ohms in the ordinary pattern of instrument. As there is no suspended...
Page 143 - ... paraffin wax. Contact with the mercury may be made by means of a platinum wire passing down a glass tube, cemented to the inside of the cell, and dipping below the surface of the mercury, or more conveniently by * It equals 1-42 (new) volt.
Page 52 - The mirror is placed in the axle of a coil of wire, some four or five inches across, which completely surrounds it, so that the needle is always under the influence of the coil at whatever angle it is deflected to. A beam of light from a lamp placed behind a screen about three feet distant from the coil falls on the little mirror, the bottom of which is slightly in advance of the top, and is reflected back on to a graduated scale placed just above the point where the beam of light emerges from the...
Page 143 - The battery is formed by employing pure mercury as the negative element, the mercury being covered by a paste made by boiling mercurous sulphate in a thoroughly saturated solution of zinc sulphate, the positive element consisting of pure distilled zinc resting on the paste. The best method of forming this element is to dissolve pure zinc sulphate to saturation in boiling distilled water. When cool, the solution is poured off from the crystals and mixed to a thick paste with pure mercurous sulphate,...
Page 64 - ... stretched ; and a screw-head at the top of the instrument serves both to regulate the tension in the wires and to let the coil down, to a position of rest on the central iron cylinder, whenever the galvanometer is to be dismounted for removal to a distant place. The resistance of the coil is about 150 ohms in the ordinary pattern of instrument. As there is no suspended needle, no external magnetic forces affect the zero of the instrument ; and, since the position of the coil is determined solely...
Page 142 - U-tube with the denser zinc-sulphate solution ; then insert the zinc rod and fit it tightly by the rubber cork P. Now, on opening the tap C the level of the liquid will begin to fall in the right-hand limb but be retained in the closed one. As the level commences to sink in the right-hand limb, by opening the tap B copper-sulphate solution can be allowed to flow in gently to replace it ; and this operation can be so conducted that the level of demarcation of the two liquids remains quite sharp, and...
Page 14 - The brass blocks, here shown in !•'". t- - . are screwed down to a plate of ebonite which forms the top of the box in which the coils are enclosed. The ebonite bobbins are fixed to the lower surface of the ebonite top, the ends of the wires being fixed to the screws which secure the brass blocks. The holes shown in the middle of the brass blocks are convenient for holding the plugs that are not in use.
Page 65 - The intensity of the magnetic field in which the coil is situated is such that whenever the galvanometer-circuit is closed — even through a considerable resistance— the motion of the needle is dead-beat. It takes less than one second to come to rest at its final position of deflection, and when it returns to zero it does so with the most complete absence of oscillations. The spot of light on the scale never oscillates so much as i millimetre over the zero on releasing the galvanometer-key.

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