Fig. 12.

The measuring or cal­i­bre-bridge (see Fig. 7) serves to de­ter­mine ac­cu­rate­ly wheth­er the ready plates have the height of type. A rule of for­ty {99} cen­ti­met­res will suf­fice for any plate. No plate should leave the work­shop with­out hav­ing been test­ed as to its thick­ness or height on this ins­tru­ment.

The zinc plane is of or­di­nary con­struc­tion, to the bot­tom of which is at­tached a doub­le lay­er of hard wood. The iron being ar­ranged for scrap­ing can be in­sert­ed in a po­si­tion just the re­verse of the or­di­nary plane.

The “hand-bridge” is a strong ru­ler, thir­ty cen­ti­met­res long, and five cent­i­met­res wide, to the ends of which are fas­tened two blocks of wood one cen­ti­met­re high. It serves as a sup­port for the hand in re­touch­ing.

The rollers of the “chemigraphist,” and also the pads, are of greatest importance. For etching by the French process we need a good, rough roller, and a faultless, smooth one; for the Vienna process only the latter is needed, in addition to a smooth, tight leather ball or pad, such as was used in the art of printing prior to the introduction of rollers. A perfectly smooth surface is obtained by covering the rollers with a dryer, and allowing them to dry in the open air. A solution of shellac with camphor, applied like furniture polish, also yields a fine surface.—J. O. MORCH.

THE BEST DRYING BOX.

After bichromatizing the gelatine sheet for printing the transfer image, I proceed with the drying in a box constructed as follows:

The box has four walls or sides of cloth, or any other stuff that allows the air to pass through, and must have a solid bottom, which will allow the attachment of a heating apparatus beneath it. In this box is a cylinder which turns on its own axle, and which can be set in rotation from the outside when the box is closed. Upon this cylinder the gelatine paper, as we may call it, is placed, and the box closed. A very equalizing drying is thus obtained, by keeping the heating apparatus under the bottom of the box constantly at a steady, uniform heat. By these means, it will be noticed:

1. That an uneven running down of the chrome-layer is avoided, and uneven drying also positively prevented in consequence of the centrifugal force.