STONE, PRESERVATION mo. The mechanical preservation of stone can be effected to a great extent by coating the surface with boiled linseed oil, or with oil-paint; but these methods are not much in favor, as they destroy the crystalline appearance which constitutes the beauty of most natural stones. As promising a better result, many experi ments have been tried, especially of late, with certain chemical solutions that are not likely to mar the inherent beauty of a stone. The substances which have been most used are those soluble silicates which we have referred to under ARTIFICIAL STONE. The earlier process of Kuhlmann consisted in coating the surface with a soluble silicate of soda or potash, whieji is also known by the names of soluble glass, water-glass, and flint liquor. This was applied with a brush, and silitieation was produced by the silica Of the solution entering into combination with the lime of the stone; but this took a con Siderable -time, so that, on an exposed front, it was liable to be washed out before the proOr hardening took place. The later process of Ransome consists in cleaning the sur face of the stone from extraneous matter, and then applying alternate solutions of the above alkaline silicate and chloride of calcium, which forms an insoluble silicate of lime in the pores of the stone. This plan has been tried with a portion of the new houses of
parliament many years ago, and is now extcusitnily used in London, Edinburgh, Glas gow; and elsewhere. Rausome's process is indeed practically the only one in use. But i the preservati6n of the houses of parliament has been the subject of inquiry since this invention was applied to them; and the committee which sat did not succeed iu discov ering any preserving agent which they felt justified in proposing. The chemists engaged iu this inquiry selected, from a vast number of proposals then made, the eollowing pro cesses. as claiming a careful investigation; 1. Application of silicates of the alkalies, in various states of concentration; 2. Application of silicates, in conjunction with various saline compounds, intended to produce double decomposition.; 3. Application of hydro fluorin or hydrosilicic acid; or their saline compounds; 4. Application of phosphoric acid and acid phosphates; 5. Applications of solutions of the alkaline earths, or their bicar bonates, in water.