HEAD RESTS.--The button head rest with chair back clip, A fig. 19--is much the best for travelling artists, as it can be taken apart, into several pieces and closely packed; is easily and firmly fixed to the back of a chair by the clamp and screw a and b, and is readily adjusted to the head, as the buttons c, c and arms d, d are movable.
Sometimes the button rest is fixed to a pole, which is screwed to the chair; but this method is not so secure and solid as the clip and occupies more room in packing. Both the pole and clip, are furnished in some cases with brass band rests instead of the button; but the only recommendation these can possibly possess in the eyes of any artist, is their cheapness.
For a Daguerreotypist permanently located the independent iron head-rest, B fig. 19, is the most preferable, principally on account of its solidity. It is entirely of iron, is supported by a tripod (a) of the same metal and can be elevated by means of a rod (b) passing through the body of the tripod, to a height sufficient for a person, standing, to rest against.
GALVANIC BATTERY.--This article is used for the purpose of giving to imperfectly coated plates a thicker covering of silver. The form of battery now most universally employed for electrotype, and other galvanic purposes, is Smee's--Fig. 20. It consists of a piece of platinized silver, A, on the top of which is fixed a beam of wood, B, to prevent contact with the silver. A binding screw C is soldered on to the silver plate to connect it with any desired object, by means of the copper wire, e. A plate of amalgamated zinc, D, varying with the fancy of the operator from one half to the entire width of the silver is placed on each side of the wood. This is set into a glass vessel, P,--the extreme ends of the wood resting upon its edge--on which the acid with which it is charged has no effect. The jar is charged with sulphuric acid, (common oil of vitriol) diluted in eight parts its bulk of water. The zinc plates of the battery have been amalgamated with quicksilver, and when the battery is set into the jar of acid there should be no action percieved upon them when the poles F, G, are not in contact. Should any action be percieved, it indicates imperfect amalgamation; this can be easily remedied by pouring a little mercury upon them immediately after removing them from the acid, taking care to get none upon the centre plate A.
Directions for use.--A sheet of silver must be attached to the wire connected with the centre plate A of the battery, and placed in the silver solution--prepared as directed below. The plate to be silvered is first cleaned with diluted sulphuric acid, and then attached to the wire, G, proceeding from the zinc plates D, D, and placed in the silver solution, opposite the silver plate attached to the pole F, and about half an inch from it. A slight effervescence will now be percieved from the battery, and the silver will be deposited upon the Daguerreotype plate, while at the same time a portion of the silver plate is dissolved.
To prepare the solution of silver.--Dissolve one ounce of chloride of silver in a solution of two ounces of cyanide of potassium, previously dissolved in one quart of water. The oxide of silver may be used instead of the chloride. This solution is put into a tumbler, or other vessel.
