above and attached below to the next plate, the successive plates being separated from each other. This board is placed in the circuit, and, by means of a metallic key which may be shifted from one of the plates to another, the full current of the machine, or any proportion of it that may be required, may be passed into

the bath.

magnet, of which the base of the machine forms a part, and which is so formed as to secure a much greater length than is commonly used. The purpose of the designer in introducing this feature is to interpose as great a resistance as possible to reversal. The opposite poles of the magnet inclose the armature which thus occupies and fills the magnetic field. The fixed magnet is wound in the usual manner; and its form is such as to allow a free circulation of air through longitudinal recesses in the outer surfaces of the core, which, when it is wound, become passages open at each end for the transmission of a current of air produced by the rotation of the armature. Much stress is laid by the maker of this machine upon the

method of constructing the armature, by virtue of which, it is claimed, the local currents produced by induction in an ordinary core are so far prevented, that the heating from this cause is very inconsiderable. The armature is wound with insulated wire in substantially the same manner as other machines; and its disposition is such that its face is surrounded by the masses of iron composing the magnets with their coils; and the endeavor has been made in its form and the relation of its parts to provide that there shall be a strong magnetic action on its sides as well as on its face, and at the same time to have a free circulation of air around it and through the recesses in the magnet in order to counteract the heat that may be developed. It is further claimed that the method of construction adopted renders it possible to leave much more space between the armature and the magnets than has usually been possible. One-eighth of an inch is allowed, and it is affirmed that up to three-sixteenths of an inch, the results obtained show a gain in power without loss of current. If this space between the armature and the magnets can be allowed without detrimental effect upon the power of the machine, it will have the advantage of avoiding the danger of actual contact between the face of the armature and the magnets, which happens in some cases by wear of the journal boxes or other causes, and with disastrous results. The commutator differs in some minor details from those commonly used. The junction of the coil wires with the segments of the com mutator is made through large copper plugs, which are "sweated" in to secure perfect contact. The segments of which it is composed are separated from each other entirely by longitudinal slits, which permit of rapid cleaning by simply passing a string through an opposite pair of the slits and working it back and forward.

The Müller Machine, which has also been introduced to a considerable extent for electro-plating in the United States, and several forms of the Siemens machine, which have been largely adopted abroad for plating as well as for the metallurgical extraction of copper on the large scale, are worthy of mention as successful machines in connection with this subject. Detailed descriptions of these, however, would needlessly lengthen this chapter, and the reader is referred for such descriptions, should they be desired, to the technical journals.

Respecting the comparative merits of these and other machines, there is much diversity of opinion among those who use them, some preferring one and others another. As remarked elsewhere, there is great need of a series of tests with these machines, in order to determine which type of machine is best adapted for electro-metallurgical purposes. Meantime, the claims of rival makers, and widely differing testimony of electro-platers, render the selection of a machine a task of no little difficulty.

In conclusion, we may be allowed to briefly reaffirm that the dynamo-electric machine has now practically become the sole source of electric current in the art of electro-plating. In one or another of its numerous modifications it has supplanted almost entirely the cumbersome, troublesome, and expensive voltaic battery. By reason of the economy, certainty, and rapidity of its oper ation it has contributed very largely to the considerable extension of the art of electro-plating, and cheapened the cost of this class of work, and it may safely be credited with having called into existence one of the most extensive and important branches of the art; we refer to nickel plating, which without its aid could never have come into general use.

CHAPTER X.

DEPOSITION OF COPPER-BY SIMPLE IMMERSION-BY

BATTERY.

Deposition of Copper.

WE have said, in the articles on cleansing, that it was often useful, and sometimes absolutely necessary, to effect a primary deposit of copper, brass, and sometimes of tin, upon common metals or alloys, such as wrought and cast iron, zinc, Algiers metal, etc., before they receive the precious metals. But these various operations are often not simply the complement of the cleansing process, but furnish products ready for the trade without any further operations. We shall carefully describe the various. formulæ, by the aid of which we arrive at these results.

Deposition of Copper (by simple immersion).

Copper deposits are obtained, according to the metals employed or the object in view, either by simple immersion or by the galvanic method.

The deposition of copper by immersion is seldom practised except upon iron, and the deposits obtained are generally wanting in lasting qualities. They are intended to please the eye only, since, from the thinness of the deposit, the iron is not protected against atmospheric influences. It may even be rendered more liable to oxidation.

We employ a bath composed of—

Sulphate of copper (blue vitriol)
Sulphuric acid (oil of vitriol).

10 parts.

10

500 to 1000 66