FIG. 342. SILVER VOLTAMETER.

In the cut Ag is the silver anode, Pt is the platinum dish, r is the conducting rod, p is a wooden standard, Cu is a copper plate on which the dish rests and which also serves as a conductor and contact surface, b is a muslin cloth to place over the silver plate to prevent detached particles falling in the dish; s s' are the binding screws. The weight of silver corresponding to a coulomb is given variously by different authorities. Ayrton and Daniell take 1.11815 milligrams or .017253 grain of metallic silver. Other determinations are as follows: 1.1183 milligrams   (Kohlrausch). 1.124 " (Merscart). The solution of silver nitrate should be from 15 to 30 per cent. of strength. The current should not exceed one ampere per six square inches; or in other words not more than about 3/1000 grain of silver should be deposited per second on a square inch area of the dish. The edge of the silver disc or anode should be about equidistant from the side and bottom of the dish. The latter notes are due to Lord Rayleigh. 566   STANDARD ELECTRICAL DICTIONARY.