Ans. A cylinder of hemp or other fabric used in place of a porous pot in some forms of Leclanche cell, and also as a support for the depolarizing mass in some forms of dry cell where the electrolyte is of a thin gelatinous nature. =Volta’s Contact Law.=--When metals differing from each other are brought into contact, different results are obtained, both as to the kind of electrification as well as the difference of potentials. Volta found that iron, when in contact with zinc, becomes negatively electrified; the same takes place, but somewhat weaker, when iron is touched with lead or tin. When, however, iron is touched by copper or silver, it becomes positively electrified. Volta, Seebeck, Pfaff, and others have investigated the behavior of many metals and alloys when in contact with each other. The following lists are so arranged that those metals first in each list become positively electrified when touched by any taking rank after them: CONTACT SERIES OF METALS _According to Volta_. _According to Pfaff._ + zinc + zinc lead cadmium tin tin iron lead copper tungsten silver iron gold bismuth graphite antimony - manganese ore copper silver gold uranium tellurium platinum - palladium Volta laid down a law regarding the position of the metals in his table which may be stated as follows: _The difference of potential between any two metals is equal to the sum of the differences of potentials of all the intermediate members of the series._ Hence, it is immaterial for the total effect whether the first and the last are brought into contact directly, or whether the contact is brought about by means of all or any of the intermediate metals. Volta’s law further asserts that when any number of metals are brought into contact with each other, but so that the chain closes with the metal with which it was begun, the total difference must be zero. =Laws of Chemical Action in the Cell.=--There are two simple laws of chemical action in the cell: 1. _The amount of chemical action in a cell is proportional to the quantity of electricity that passes through it._ One coulomb of electricity in passing through the cell liberates .000010352 of a gramme of hydrogen, and causes .00063344 of a gramme of zinc to dissolve in the acid. 2. _The amount of chemical action is equal in each cell of a battery connected in series._ =Requirements of a Good Cell.--=The several conditions which should be fulfilled by a good cell are as follows: