Electrometallurgy

Art of precipitating metals from the solutions of their salts by an electric current. The metal is deposited on the negative pole, while the acid becomes free at the positive. The proce was discovered by Spencer in England, and independently by Jacobi in St. Petersburg in 1839. The art is sometimes called Galvanoplastics. Electrometer. Instrument for directly measuring the difference of electrical potential between two points. The quadrant electrometer of Sir W. Thomson consists of a hollow metal cylindrical box divided into four quadrants, separated from one another by a small space. Each pair formed by two opposite quadrants are joined together by a wire, but insulated from the other and adjacent pair. Within the box and suspended by a silk fiber, Carpenteir's Quadrant Electrometer. the suspending fiber. This angle is usually measured by the deflection of a spot of light reflected from a small mirror attached to the suspension.