tact with its contents. The negative plate consists of a grid of cold-rolled steel, also heavily nickel-plated, holding a number of rectangular pockets filled with powdered iron oxide. These pockets are also made up of finely perforated steel, nickel-plated. After the pockets are filled they are inserted in the grid and subjected

to considerable pressure between dies, which corrugate the surfaces of the pockets and force them into positive contact with the grids.

These elements are housed in a jar or container made from

Fig. 18.-Part Sectional View of Edison Alkaline Battery, Showing Internal Arrangement of Plates and Relation of Principal Parts to Each Other.

cold-rolled steel, which is thoroughly welded at the seams and heavily nickel-plated, as shown at Fig. 18. The plates are assembled in positive and negative groups by means of threaded steel rods passing through holes in one corner of the plates and insulating washers. The terminal post is secured to the middle of the rod. The complete element or plate assembly stands on hard rubber bridges on the bottom of the can, and is kept out of contact with the sides of the container by hard rubber spacers attached to the end. The can cover is also of sheet steel, and contains fittings through which the electrodes pass, these being insulated from the cover by bushings of insulating material. A combined filling aperture and vent plug is secured to the center of the cover plate. The general arrangement of the Edison cell parts is clearly outlined at Fig. 18; the plate construction is depicted at Fig. 19, as well as the tubes from the positive plate and pockets used in the negatives.

Function of Separator.-Separators are necessary to keep plates of opposite polarity apart, and yet the space between the plates should be as small as possible in order to keep the internal resistance of the cells to a low point. It is apparent that current used to overcome internal resistance cannot be used in the external circuit. Separators may be of rubber, glass or wood. Perforated rubber sheets have been used, but these are not considered as good as wood separators, and are usually used in connection with them. Glass separators are used only in the largest cells, and usually consist of a series of vertical rods between the plates. Wood is used on all small cells. The material is specially selected and chemically treated. They are made very thin, and after cutting from seasoned wood they receive treatment to remove any elements that might cause damage if left in the wood. Thereafter, the separator strips are kept soaking in a weak electrolyte solution until they are installed in batteries. They must never be allowed to dry out, and even in transit from factory to service station they should be packed in such a way as to retain their moisture.

In impressing this matter on users of their batteries, the U. S. L. and H. Co. gives the following suggestions: "The owner must likewise do his part with the water cure as outlined above, to

prevent the separators from drying out in service. Once dried out a separator can never again, with or without water, be the same, but loses its vitality and is prone to split and undermine the battery's health. A badly shattered separator, of course, invites a direct short circuit, with resultant internal discharge of the cell. But battery plates seem eager to get together, and even a split in

Alkaline Battery.

a separator affords the opportunity for 'treeing' across from negative to positive. That is, a foliage-like formation develops on the negative and extends through any available opening until it reaches the positive, and the short circuit thus produced not only dissipates the energy of the battery but to a greater or less degree cripples the battery. It also furthers the possibility of sulphation. The necessity for high capacity in starter batteries within little space demands that the plates shall be but a short distance apart. Thus, unless prevented by special provision, 'treeing' would occur across the bottoms of the separators. In assembling U. S. L. batteries pains are taken to make the separators of such length and to so fit them in place that their bottoms shall extend below the plates. Trouble has been experienced from distortion of the grids and the chiseling off of the separator bottoms by the sharp plate edges in their distorted condition. Buckled plates are saucershaped, so that the old-fashioned square-cornered plates did the most chiseling with their corners. To minimize the effects of buckling, even though it be the result of abuse, U. S. L. plates are round-cornered."