Part 10 (1/2)

PLATING IRON WITH COPPER--We have room in this chapter for only one concrete example of this work, which, with suitable modifications, is an example of the art as practiced co coated with copper to preserve it fro dynae, of course, depending upon the surface to be treated at one time The pressure should not exceed 5 volts

The iron surface to be treated should first be thoroughly cleansed, and then i a cyanide of copper solution Two forms of copper solution are used, namely, the cyanide, which is a salt solution of copper, and the sulphate, which is an acid solution of copper Cyanide is first used because it does not attack the iron, as would be the case if the sulphate solution should first come into contact with the iron

A sheet of copper, termed the anode, is then placed within the tank, parallel with the surface to be plated, known as the cathode, and so mounted that it may be adjusted to or from the iron surface, or cathode

A direct current of electricity is then caused to flow through the copper plate and into the iron plate or surface, and the plating proceeded with until the iron surface has a thin film of copper deposited thereon This is a slow process with the cyanide solution, so it is discontinued as soon as possible, after the iron surface has been cohly cleaned off to remove therefrom the saline or alkaline solution, and it is then i a solution of sulphate of copper The current is then thrown on and allowed so to remain until it has deposited the proper thickness of copper

DIRECTION OF CURRENT--If a copper and an iron plate are put into a copper solution and connected up in circuit with each other, a prienerate electricity In this case, the iron will be positive and the copper negative, so that the current within such a cell would flow froative, or cathode

The action of electroplating reverses this process and causes the current to flow from the copper to the iron (in this instance, the cathode)

CHAPTER XIV

ELECTRIC HEATING, THERMO ELECTRICITY

GENERATING HEAT IN A WIRE--When a current of electricity passes through a conductor, like a wire, more or less heat is developed in the conductor This heat may be so small that it cannot be reater or less degree Conductors offer a resistance to the passage of a current, just the sah which it passes This resistance ischapter, and it is this resistance which is utilized for electric heating

RESISTANCE OF SUBSTANCES--Silver offers less resistance to the passage of a current than any other metal, the next in order is copper, while iron is, co is a partial list oftheir relative conductivity:

Silver 1

Copper 104 to 109 Gold 138 to 141 Aluminum 164 Zinc 379 Nickel 469 Iron 656 Tin 89 Lead 132 German Silver 122 to 15

From this table it will be seen that, for instance, iron offers six and a half times the resistance of silver, and that German silver has fifteen times the resistance of silver

This table is made up of strands of the different ths, so as to obtain their relative values

SIZES OF CONDUCTORS--Another thing, however, must be understood If two conductors of the sa different diameters, receive the sareater resistance than the large conductor, hence will generatethe diameter of the conductor The metal used is, therefore, of importance, on account of the cost involved

COMPARISON OF METALS--A conductor of aluht as copper, has a diareater than copper; but as the resistance of aluminum is 50 per cent

ht for weight, copper is the cheaper, particularly as aluminum costs fully three ti 96_ SIMPLE ELECTRIC HEATER]

The table shows that Gerhest resistance Of course, there are other metals, like antiher resistance Gerh there are various alloys of h resistance and are cheaper

The principle of all electric heaters is the sae of a current, and an illustration of a water heater will show the elementary principles in all of these devices

A SIMPLE ELECTRIC HEATER--In Fig 96 the illustration shows a cup or holder (A) for the wire, made of hard rubber This may be of such dialass (B) The rubber should be 1/2 inch thick Two holes are bored through the rubber cup, and through the 1-1/2 inches long, so they will project an inch below the cap

Each screw should have a small hole in its lower end to receive a pin (E) which will prevent the resistance wire fro off

The resistance wire (F) is coiled for a suitable length, dependent upon the current used, one end being fastened by wrapping it around the screw (C) The other end of the wire is then brought upwardly through the interior of the coil and secured in like manner to the other screw (D)