When one of these is added to a sulphuric acid solution, using zinc and carbon as the battery elements, it forms a very powerful cell, having E. M. F. of two volts. A battery solution of this kind may be prepared by adding four ounces of bichromate of potash to a solution composed of four ounces of sulphuric acid mixed with sixteen ounces of water. The battery will give a more powerful current for a longer time when this solution is used instead of the plain sulphuric acid and water or sal ammoniac. [Illustration: Fig. 63.—A Battery Element arranged for three Cells.] It might be well at this time to caution the experimenter against the careless handling of sulphuric acid. It is not dangerous if handled properly, but if spilled or spattered around carelessly it is capable of doing considerable damage to most things with which it comes in contact. Do not attempt to use it in any place but a shop or cellar. The smallest drop coming in contact with any organic matter such as woodwork, clothing, carpets, etc., will not only discolor any of the latter, but eat a hole in it. The best thing to use to counteract the effects of the acid which has been spilled or spattered is water in sufficient quantity to drench things and dilute the acid enough to render it harmless. A little strong ammonia will neutralize the acid and sometimes restore the color to clothing which has been burned by acid. [Illustration: Fig. 64.—A Plunge Battery, with Windlass.] All acid batteries of this sort have the one objection that it is impossible to leave the elements in the solution without wasting the zinc. The usual way to arrange the battery cells so that the elements may be removed from the solution most easily is to fasten the elements to a chain or cord passing over a windlass fitted with a crank so that when the crank is turned the elements may be raised or lowered as desired. A "plunge battery" of this sort is illustrated in Figure 64. The construction is so plainly shown by the drawing that it is hardly necessary to enter into the details. The crank is arranged with a dowel-pin which passes through into a hole in the frame, so that when the elements are lifted out of the solution the pin may be inserted in the hole and the windlass prevented from unwinding. [Illustration: Fig. 65.—A Plunge Battery adapted to a Set of Elements, as shown in Figure 63. They may be lifted out and placed on the "Arms" to drain.] A somewhat easier method of accomplishing the same result is that shown by Figure 65. In this, the elements are simply raised up out of the jars and laid across the two "arms" to drain. *The Edison-Lalande* cell employs a block of pressed copper oxide as the positive element, while two zinc plates form the negative. The exciting liquid is a strong solution of caustic soda. [Illustration: Fig. 66.—An Edison-Lalande Cell.]