It has already been shown how cells become "polarized" when the solution consists simply of sulphuric acid and water. An ordinary acid solution also has the further disadvantage that the zinc element is continually consumed by the acid when it is in the solution, regardless of whether current is being drawn from the cell or not. It is of course consumed more rapidly when the circuit is complete and current is flowing than when it is not, but the action is still nevertheless sufficiently rapid to entirely consume the zinc even in the latter case in a very short time. If an ordinary acid solution is used therefore as the liquid or *electrolyte*, as it is technically termed, it is always necessary to lift the elements out of their solutions whenever the cells are not in use. They should be lifted out and carefully washed so as to remove all traces of acid.
[Illustration: FIG. 32.—A Battery of Three Cells arranged so that they can all be lifted out of the solution at once.]
A milder chemical which does not attack the zinc so rapidly as an acid is often used wherever a battery is to be employed for ringing bells, operating sounders, telephoning, etc., and only a small amount is required.
Sal-ammoniac or chloride of ammonium, as it is also called, is a good chemical for this purpose. It is very cheap and only requires to be dissolved in water. A good strong solution should be made and an element consisting of several carbons and one zinc such as those shown in Figures 29, 30 and 31 used.
Such a cell will give about 1.5 volts and 3 or 4 amperes. If the current is drawn from the battery continuously or too rapidly, it will also *polarize* and the current will begin to fall off. The advantage of a sal-ammoniac cell is that the elements may be left in the solution when the cell is not in use, without appreciable waste of the zinc.
A very powerful cell of the non-polarizing type capable of delivering a heavy current and having an E. M. F. of two volts can be made by adding some potassium bichromate to a sulphuric acid solution.
An electrolyte of this sort may be prepared by dissolving four ounces of bichromate of potash in sixteen ounces of water. Add to this, four ounces of sulphuric acid. The acid should be added slowly and the solution stirred at the same time.
This solution will be found an excellent one to use with cells having carbon and zinc elements. The current and voltage are much higher than those of an ordinary acid solution.
This type of cell also has the disadvantage that the zincs waste away rapidly when in the solution, regardless of whether current is being drawn or not. This can be partly overcome by *amalgamating* the zincs with mercury. In order to amalgamate your battery zincs, procure a little *mercuric nitrate* from a druggist or chemical house. Dissolve the mercuric nitrate in a small amount of water and then rub the zincs with a wad of cotton or cloth which has been dipped in the mercuric nitrate solution.
The arrangement shown in Figure 32 is a very convenient one to follow in arranging a battery of three or more cells. The elements of three cells are all mounted upon a strip of paraffined wood and connected in series. The three battery jars are placed in a row so that each pair of elements will dip into their proper jar when the strip is laid across the tops.