If we have an ordinary gelatine negative, say, of half-plate size, and require to enlarge it to a whole plate, the simplest plan is to thoroughly wash it and immerse in a solution composed of citric acid, 2 ounces; hydrofluoric acid, 1 ounce; acetic acid (glacial), 1 ounce; glycerine, 1/2 ounce; water, 20 ounces. The action of the hydrofluoric acid will be to detach the film from the glass, while the other acids will cause the film to spread out considerably; the action being even all over, the image is completely enlarged. It is then carefully removed and washed in plenty of clean water, after which it can be transferred to a larger piece of glass. The action is sometimes to weaken the negative in density; it is therefore occasionally necessary to intensify it.