In one of these cases, which was settled before it reached the courts, a letter which was to be put in evidence in a dispute as to some property had originally contained the words "your house," but the "y" had been skilfully erased, so that the words read "our house." When the paper was held to the light it showed an almost imperceptible thinness at that place, but under the microscope the ruffled fibres on the surface of the paper where the sizing had been scratched off, were very noticeable. Skilful forgers guard against this obvious sign of alteration by treating the erased place with a solution of rosin in spirit, which leaves a fine shiny layer upon the paper similar to that of the original sizing. A treatment first with hot water and then with alcohol will remove this coating of glue or rosin, and when the paper has been dried again it will be found that this part, which will now be free from its protective layer, will absorb a drop of water more rapidly than the rest of the surface. Another simple test to reveal erasure is the use of iodine vapour, which will often cause a blue coloration (due to starch) upon the moistened surface from which sizing has been removed, but will only colour the remainder of the paper brown. This test gave a very pronounced result in the examination of the letter to which reference has been made, in which erasure of the letter "y" had been suspected from the general appearance and microscopical examination of the surface of the paper. The course of the tests described above should be followed under the microscope, although in some instances the fraud is so extensive as not to require any magnification. As a rule, however, it is preferable to use only one drop of a reagent, and to follow closely under a low power of the microscope, its action, both upon the material of paper and upon the ink of any writing, which it may render visible. The detection of mechanical erasure, which as was mentioned above, is frequently indicated by the paper being thinner and more transparent at that place, is often rendered more certain by photography. Thus if the document on which was the suspected erasure is placed between a strong light and the camera, the negative will show a darker area corresponding to the place where more light was transmitted through the paper. A photograph taken in direct light would probably in such a case show nothing, but in a negative taken with the light falling obliquely upon the paper, the fibres that had been roughened by the erasure would be visible, unless a subsequent treatment with glue or rosin had been used to conceal the injury to the surface.