The celluloid of which the isolators are made are not attacked by the electrolyte at ordinary temperatures. At higher temperatures, however, the electrolyte slowly dissolves the isolators. The condition of the isolator, therefore, may be used to determine whether the temperature of the electrolyte has been allowed to rise above 100° Fahrenheit.
The Vesta Type "D" Battery
The appearance of a group of the new Type "D" construction is shown in Fig. 265, where Type "C" and Type "D" groups are illustrated side by side for purposes of comparison. It will be seen that the "D" isolator is of one piece only (shown separately in Fig. 266). The material is a heavy hard rubber stock which will be no more affected by acid or by electrical conditions in the cell than the hard rubber battery jar itself. The indentations on the two edges of isolator engage in hook shaped lugs on plate edges (Fig. 267 shows these clearly) and lock the plates apart fully as efficiently as the three-piece construction.
There are a number of important advantages which have been gained by the new method of isolation. The illustration (Fig. 265) shows how the "D" isolator permits the separators to completely cover and project slightly beyond the edges of the plates, whereas in the old construction there is an edge just above the isolators where the plates are not covered. This improvement means protection against shorts due to flaking, always so likely to occur during the summer "overcharging" season. Overcharging is, of course, a form of abuse, and Type "D" batteries are designed to meet this sort of service. Another great advantage gained is in the arrangement of lugs, It will be noted that the positive isolator hooks are in alignment, as are the negative hooks, but that these two rows, of opposite polarity, are separated from each other by the full width of the isolator; whereas in the Type "C" construction the outer edges of the plates, of opposite polarity, were separated only by the usual distance between plates.
The new isolator is simple to insert and remove. Being made of hard rubber, it will soften and become pliable if a sufficient degree of heat is applied. The heat required is approximately 150° to 160°F., a temperature far above that reached by any battery cell, even under the most extravagant condition of abuse, but readily attained in the shop by means of a small flame of any kind-even a match will do in an emergency. The flame (which should be of the yellow or luminous variety, as the blue flame tends to scorch the rubber) is played lightly over the isolator a few seconds. The rubber becomes soft and is then removed by inserting under the end of the isolator any narrow tool, such as a small screw driver, a wedge point, chisel, etc., and prying gently. In replacing isolators, a small hot plate is convenient but not at all necessary. The isolators are placed on the hot plate, or held in a luminous flame, until soft enough to bend. They are then bent into an arched shape, as shown in Fig. 268, and quickly fitted into place under the proper lugs. The regular isolator spacing tool is convenient and helpful in maintaining the plates at uniform intervals while this operation is carried out. The job is completed by pressing down the still warm isolator with any handy piece of metal having a flat edge that will fit the distance between the lugs (Fig. 269). The shank of a screw driver does splendidly for this work. The pressure causes the isolator to straighten out, and the indentations fit snugly under the respective hooks on the plates. At the same time the contact with the cold metal chills the rubber to its normal hard condition. It is especially to be noted that the entire operation of isolator removal and replacement can be carried out with none but the commonest of shop tools.
