STONE, ARTIFICIAL. Artificial stone, properly speaking, would include burned clay wares used for building purposes. as bricks, terra-cotta (q.v.), etc., as well as the various cements. We shall confine ourselves here to a description of the silicions artificial stone produced by the cementing properties of soluble alkaline silicates on sand, which has excited a great deal of attention within the last 30 years. So far back as 1825. prof. J. N. von Fuchs of Munich published a paper ou various applications of these silicates, and so laid the foundation of a new industry. To M. Kuhlmann of Lille, however, is mainly clue the merit of working out the practical application of the soluble silicate of potash or soda to the manufacture of hydraulic lime. cement, and especially to artificial stones. Mr. Frederick Ransome of Ipswich has also done great service by his success ful exertions in producing an artificial stone from the same substances. The process, as at first practiced by Mr. Ransomo, consisted in mixing the gelatinous silicate of soda with • sand and a little powdered glass and clay, in the proportions of sand, 10 parts; glass, 1. part; clay, 1 part; and silicate of soda, 1 part. These ingredients were thor oughly incorporated in a pug-mill, and brought to the consistency oeputty. The plastic ,nature of the substance at this stage allows it to be molded with ease into an endless variety of forms, even of an elaborately ornamental kind. After leaving the molds, the objects are dried in close ovens, and then removed to kilns, where they are fired at a gradually increasing temperature, which finally reaches a red heat. In the kiln, the goods are bedded up in dry sand, to prevent any of the twisting or loss of shape which so com monly disfigures large objects in baked clay. When the firing is completed, the material is in the state of a semi-vitrified mass, with the appearance, properties, and composition of a fine sandstone.
A later patent of Mr. Ransome's consists in producing a hard and durable material altogether without baking, by effecting a double decomposition with the silicate of soda and the chloride of calcium. Such materials as sand, chalk, or other minerals are inti mately mixed with a proper quantity of a solution of silicate of soda, this being secured, as before, by the operations of a pug-mill. In this plastic condition, they are molded into any required form, after 'which they are saturated with a solution of chloride of cal cium. The silica combining with the calcium forms at once an insoluble silicate of lime, which cements into a firm mass all the particles of sand, lime, etc., used in the composition. The chlorine, on the other hand, combines with the soda to form com mon salt (chloride of sodium), which can be readily removed by washing.
In order to avoid the difficulty experienced in removing all traces of chloride of cal cium from artificial stone made by this last process, Mr. Hansome in 1872 succeeded in making a very compact stone by mixiug lime and a natural soluble silica found in a rock forming a stratum of the lower chalk in Surrey with sand and silicate of soda. In point of strength this material excels Portland stone, not breaking so readily by a given transverse strain.
The objects into which artificial stone is manufactured are very miscellaneous; what ever, in fact, is made of real stone can also be formed in the artificial. Among the more prominent applications of it, we may notice grindstones, millstones, tombstones, monu ments, chimney-pieces, balustrades, fountains, vases, and statuary.