The advance of photography : its history and modern applications (1911)

102 THE ADVANCE OF PHOTOGRAPHY Therefore, if any colouring matter in powder form be strewn over the film after exposure, it adheres where the strokes of the drawing have protected the film from the light, but not at other places, and thus a picture in powdered colour is obtained. If this coloured powder and the surface on which it is strewn are fire-proof — as glass and porcelain — the picture obtained can be burnt in, and pictures of various shades can be produced, according to the choice of the powdered colour. Pictures of this kind can be transferred from one surface to another. If a collodion film is poured upon the powdered picture and suffered to dry, and then the whole immersed in water, the collodion film with the picture can be easily separated from the surface on which it was produced, and transferred to and burnt into other surfaces — glasses, cups, etc. The PeaSausage. — In the Franco-German campaign of 1870, the well-known pea-sausage 1 was one of the most important articles of food for the army, and was prepared daily by thousands. The fabrication of the interior portion caused little difficulty, but the obtaining so many skins created much difficulty. As the supply fell short, a substitute was sought in vegetable parchment. This paper, which is produced by dipping blotting-paper in sulphuric acid for about a second, then washing and drying, is distinguished by its skin-like properties of resistance. It is impenetrable to water, and difficult to tear. It is therefore used for the production of bank-notes. It was attempted to make sausage skins of this paper, by doubling a sheet cylindrically and pasting it together. No glue or gum can, however, resist the effect of the boiling water in which the sausage has to be cooked, and so the artificial sausage skin fell asunder. Dr Jacobson solved the problem by producing an adhesive substance, with the help of the chemical action of light, which could resist 1 Erbswurst.