[O] Transfer paper is more reliable. If the transfer should exhibit any signs of weakness while the stone is still covered with plain gum water, take, upon a small linen pad, a little ink thinned either with tallow or a few drops of turpentine; by careful rubbing in different directions the lines will be considerably strengthened. Plenty of gum must be kept upon the surface of the stone during this operation, at the completion of which it may be removed with a sponge and water, and the inking-up completed with the roller and the stone gummed in. Before printing, the gum has to be removed by water, and the stone rolled up with a moderately stiff ink; it is then etched with gum water rendered slightly acid by a few drops of nitric acid. The best test for the acidity of this solution is to add just so much acid to the gum water that, after its application to the edge of the stone for two or three seconds, scarcely perceptible bubbles of carbonic acid gas will show. This is applied evenly to the drawing with a sponge, and allowed to act for a few seconds. Should the ink “take” to the stone in places other than the design or writing, rub the spot at once with woollen material moistened with gum water; this will clear away the superfluous ink, but the part should be carefully watched during the printing for any recurrence. After the removal of each impression the stone is damped over the whole surface with a damping cloth before another application of the inking roller. For the production of perfect impressions avoid contact of the hands with the face of the paper or stone, and care must be exercised that all matters connected with the printing are kept scrupulously clean, any contamination of a fatty or greasy nature especially being strenuously avoided. The paper used in lithographic printing is usually slightly damped by placing between sheets of damp blotting paper; such proceeding is not absolutely necessary, as dry sized paper may also be used. The above detailed description of the necessary sequence of operations in the Autographic transfer process will assist in understanding that of photo-lithographic transfer, which requires still more care, and the use of a special transfer paper so prepared that it is sensitive to light. THE BITUMEN METHOD.