Fig. 9 represents Talbot's Calotype Camera,--a very beautiful instrument.
The copying camera box has an extra slide in the back end, by which it may be considerably lengthened at pleasure.
II.--CAMERA STAND.--The best constructed stands are made of maple or black walnut wood, having a cast iron socket (a, Fig. 12,) through which the sliding rod b passes, and into which the legs c, c, with iron screw ferules are inserted. The platform d is made of two pieces, hinged together, as at e, and having a thumb screw for the purpose of elevating or depressing the instrument.
III. MERCURY BATH.--Fig. 13 gives a front view of the mercury bath now in general use in this country for mercurializing and bringing out the picture. It is quite an improvement on those first used. To make it more portable it is in three pieces, a b and c; having a groove e on one side to receive the thermometre tube and scale by which the proper degree of heating the mercury is ascertained. Into the top are nicely fitted two or three iron frames, with shoulders, for the plate to rest in, suitable for the different sizes of plates. The bath is heated by means of a spirit lamp placed under it. From two to four ounces of highly purified mercury are put into the bath at a time.
IV. PLATE BLOCKS AND VICES.--There are several kinds of this article in use; I shall describe the two best only.
Fig. 10 gives an idea of the improvement on the English hand block. The top a is perfectly flat and smooth--a little smaller than the plate, so as to permit the latter to project a very little all around--having at opposite angles c c two clasps, one fixed the other moveable, but capable of being fastened by the thumb screw d, so as to secure the plate tightly upon the block. This block turns upon a swivle, b, which is attached to the table by the screw c, This block is only used for holding the plate while undergoing the first operation in cleaning.
