Portable Bat Smee's elements, packed into a handsome mahogany Foveaux's box, which measures in length 14 inches, in breadth, tery. 7 inches, and in height 101 inches (fig. 4). The cells containing the exciting fluid (diluted sulphuric acid), and which are constructed of porcelain, are attached to an ingeniously devised lifting arrangement. When the lid of the box is closed, and the battery is out of use, the cells and the contained exciting fluid are depressed beneath the elements, and the latter are no longer immersed. When the lid of the battery is raised to place the instrument in use, the cells are elevated and the elements immersed. By this arrangement the zinc is withdrawn from the destructive action of the acid when the apparatus is not in use, and the waste of the elements may be obviated to the greatest extent. Foveaux's tery. It requires, in constant daily use, to be charged about once in two months, by pouring into each cell a measured portion of diluted sulphuric acid (one part of strong acid to twenty-nine of water). A measure holding the requisite amount of acid is supplied with the instrument. To charge it the plates can be lifted out of the cells en masse, as shown in fig. 5, without any trouble in dismounting them. The elements being lifted out, the arrangement of the cells is seen in fig. 6. By means of a dial plate with a moveable needle, the current is graduated without detaching the conducting wires. The battery is mounted in sizes varying from twenty to sixty cells, and in price from 67. to 157. 15s. The more generally useful sizes contain thirty and sixty elements. I have used Foveaux's Portable Bat battery chiefly in cases in which the interrupted Foveaux's voltaic current has been required to be used for tery. diagnostic purposes. It is an exquisitely made instrument, and fully supplies a long felt want. tery. Stöhrer's Battery with Lifting Apparatus.-Stöhrer Stöhrer's Batof Dresden has constructed a very excellent battery for medical purposes. The elements, consisting of carbon and zinc, are attached in pairs to a wooden rail, and project into glass vessels, which serve for the reception of diluted sulphuric acid, and which are so arranged in the completed apparatus, that they can be moved vertically up and down, and fixed in either position. By this arrangement the acid can be brought into contact with the zinc and carbon, or by shutting down the cells be excluded from them altogether. In the latter case the acid will only fill the lower third of the glass, and it is hardly possible that it can be spilt. Should, however, such an accident be apt to occur, a small stopper of caoutchouc at the left side of the base must be pulled out, and the instrument slightly inclined, that the acid may run out. The conducting cords are attached, as shown in figs. 7 and 8, to a simple and easily adjusted slide running in a groove upon the bar that supports the elements, and at its lower surface being in metallic connexion with them. By the movement of the slide any desired number of cells can be brought into operation; and on its upper surface is an ingeniously devised commutator, by tery. Stöhrer's Bat- turning which to the right or left, the current admits of being reversed without removal of the conductors. The bar is marked from left to right with cyphers corresponding with the number of the elements, and their points of attachment, and it is of importance that the centre of the slide should be placed in a line with this attachment, as shown in fig. 7, in which fourteen, and in fig. 8, in which ten cells are in use. If this rule is neglected, rapid decomposition with development of gas, weakening of the current and general fouling of the instrument will result. In frequent use, re-amalgamation of the zincs will be required about once in six months, or whenever during use effervescence of the acid is perceived. tery. To re-amalgamate the zincs allow each plate to Stöhrer's Batremain for about a minute in diluted sulphuric acid (one part of strong acid to seven parts of water) for which purpose a common tumbler answers well. Hold the plate over a second empty tumbler, and pour upon it about a teaspoonful of quicksilver. C |