Publisher's Synopsis
This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1909 edition. Excerpt: ...value, showing that the hot wire at this low pressure gives off negative electricity. In order of course to detect this the potential on ab must be negative and this should be carefully experimented on about the reversal point. When the low pressure, at which the negative electricity is given off, is reached keep the pressure constant and measure the ionization current for different potentials between ab and PR and plot the current-voltage curve in the usual manner, which will be found to resemble the usual form of saturation curve. If the platinum wire has not been heated before it will be found necessary to keep continuously pumping out the vessel at the low pressures to maintain the pressure constant, as the heating of the wire causes it to give off occluded gases which increase the pressure in the vessel. Similar measurements may be made with a fine copper wire in place of the platinum. 74. Heated Carbon.--Similar phenomena at ITI low pressures may be observed in the case of _""0'"' heated carbon. The carbon filament from a small incandescent lamp may be utilized for this purpose. The thick filament from an 8-volt lamp will be found suitable, and it may be used without removing it from its fixtures in the lamp by breaking off the top of the lamp A (Fig. 48) and then carefully joining on a wide glass tube T which has first been drawn down to a smaller diameter and joined on to the tip of the lamp. After the joint is made it may be carefully blown out to a larger size so as to admit the electrode B, which surrounds the filament C. This electrode B consists of an aluminium cylinder which is supported by a rod sealed through the glass tube D. On the other end of D a bulb E is blown and the joint between this bulb E and the...
