I reasoned from this that oil suffered a change from exposure to air, and by combining itself presumably with oxygen acquired a more earthy character. This deduction may be correct or not; but it led me to experiment with oil as a binder for various earthy substances, because I reasoned that such a composition would be insoluble in water. The only question, then, would be if despite the intermixed oil it would permit itself to be prepared, that is, if it could be made resistant to other fats. The result justified my hopes so thoroughly that I am convinced now that with various compositions of clay, chalk, linseed oil, and metallic oxides a stone-like mass can be made that is excellent for coating paper, linen, wood, metal, etc., and thus for making plates that not only replace the stone for printing, but in many cases are far superior to it. I shall give the world a book soon about these fortunate attempts of mine, and thus perhaps give expert chemists an opportunity to perfect my invention still more. VII CHEMICAL PRINT ON METAL PLATES All metals have great inclination for fats; but if they are quite clean, being ground with pumice, for instance, or rubbed-down with chalk, they can be prepared like a stone, that is, they acquire the property of resisting oil color, thus becoming available for chemical printing. Iron and zinc can be prepared like the stone with aquafortis and gum. To prepare zinc and lead, aquafortis with nutgall and gum will serve, but a slight admixture of blue vitriol will make still a better preparation, and this in a degree that improves according to the amount of copper that the surface acquires from the coating. The most durable preparation for lead and zinc is a mixture of aquafortis, gum, and nitrate of copper. Brass and copper are best prepared with aquafortis, gum, and nitrate of lime, all mixed in proper proportions. Lime and gum are a good preparation for all metals; also potash with salt and gum. This alkaline preparation, however, is applicable only for the intaglio style. For the relief style, the acids are better. Recently I have applied chemical printing from metal plates to a new form of copying-machines, with which everything written or drawn with chemical ink or crayon on paper can be transferred in a few moments and manifolded several hundred times. His Royal Majesty of Bavaria has had the supreme condescension to grant me a six years' patent on this invention. Until now I have not been able to give this matter the necessary attention because the work of publishing this book hindered me; but now I shall make such a stock of these simple, convenient, and so widely useful hand-presses that it will be worth while to open a subscription, which would enable me to sell them for a low price. This would please me best, as my highest reward would be the general use of my inventions, to fulfill which desire I have taken the utmost pains in this work.