In a single liquid potash bichromate pile, the elements to be renewed are the zinc and the liquid which contains at once the excitant (sulphuric acid) and the depolariser (potash or soda bichromate). In order to obtain an easy renewal of the zinc, Hospitalier employs the metal in the form of a rod 18 in. in length that dips for about 3 in. only into the liquid, and that is placed in a perforated porous vessel which supports it and prevents all contact with the carbon. A certain mobility is secured to it by means of flexible attachments, so that as it wears away it descends into the liquid. Its lower extremity dips into a mass of mercury, and this keeps it amalgamated. When one rod is used up, another may be substituted for it in a few seconds. The remaining portion of the old zinc is thrown into the porous vessel. The mercury suffices to set up a perfect electric communication with the new rod that has just been introduced. The zincs are thus entirely utilised. The flow secures the continuous renewal of the exciting and depolarising liquid. The precaution to be taken is to cause the liquid to enter at the upper part, and to remove it from the lower. This prevents the elements from getting choked up, and so they may remain mounted several months, operating day and night, without any attention having to be paid to them. The positive pole consists of three or four carbon plates which surround the porous vessel that contains the zinc, and which are connected with each other by a strip of copper and screw clamps. The connection of a zinc with the following carbon is made by means of flexible wires, in order to permit the zinc to descend into the liquid as it wears away, as has already been seen. The four elements are mounted one above another. The liquid enters them from an earthenware reservoir of 5-6 gal. capacity, through a rubber tube. The discharge is regulated by means of a pinch-cock. Practice has shown that it is useless to make the solution of bichromate. It is only necessary to throw some crystals into the upper reservoir and to pour into the latter some water, acidulated with a tenth of its volume of sulphuric acid. A sufficient quantity of the salt dissolves every time to assure depolarisation. The same liquid may serve 10-12 times before renewal. There are no precise directions to be given as to the velocity of the discharge, since this must vary according to the needs of consumption. A good average is 1-1½ gal. per day. When the liquid is nearly exhausted, it is well to cause it to circulate a little more quickly. The regulation of the velocity of the flow by the Mohr pinch-cock is one of the simplest operations. After traversing the four pile elements in succession, the liquid enters glass bottles of 2 gal. capacity provided beneath with a pipe to which is affixed a rubber tube. It is only necessary to take a full bottle, place it over the reservoir, and put the pipe into the reservoir, in order to empty it in a few minutes.