MECHANICS AND USEFUL ARTS. 107 



hours on the tile, becomes hard. The superfluous clay is scraped off, 

 and the surface mechanically cleaned and smoothed, and the tile is 



tf 



then baked in the oven. This process is almost similar to the mediaeval 

 one, and Mr. Minton is entitled to the credit of having revived it with 

 increased beauty and utility. 



The mosaics are made from stained dry clays, which are pressed 

 and baked, and afterwards formed into moulds by mixing with plaster 

 or Roman cement. The pressure exercised to form these dry tiles is 

 immense, being, in the steam machine working by Prosser's patent, 

 equal to 400 tons. Each machine can make 5000 tiles an hour, and 

 but one man is required to take out the finished article. 



Lava Ware. This is the name of a new article of manufacture, 

 exhibited at the Crystal Palace, made from iron-slag, the waste of 

 smelting furnaces. After the iron is drawn off, the melted sand and 

 clay, mixed with iron, which remains as waste, greatly in the work- 

 men's way, can be cast into tiles, urns, bowls, table-tops, and various 

 useful things, at a very small cost. 



RAXSOME'S ARTIFICIAL STOXE. 



THERE has been introduced of late years a new kind of artificial 

 stone, which, although perfectly plastic at one stage of the manufac- 

 ture, is of perfectly uniform composition, entirely free from all shrink- 

 ing and contortion during the process of kiln-drying, and bears ex- 

 posure to winter temperatures and a moist atmosphere without any 

 deterioration. This important immunity from so serious an evil, it 

 owes to the fact that no part of the material used in the construction 

 consists either of lime or clay. It is, in fact, a silicious or flinty stone, 

 the particles of which it is made up (fine pure sand) being united to- 

 gether by a fluid which, after exposure to the kiln, becomes changed 

 into a kind of glass. By the very nature of the case, therefore, this 

 stone is secured from ail injury from soot, acid, or other vapors, or 

 disintegration by weather; and, in many cases where it has been 

 actually exposed for several winters, it retains all its sharpness and sur- 

 face perfectly. This material is called " Ransome's Patent Silicious 

 Stone ;" and is tolerably well known by most architects and builders, 

 as well as those engaged in ornamental stone-work. The chemical 

 fact on which the discovery of this stone is based is the perfect solu- 

 bility of flint, or any silicious material, when subjected to the action 

 of caustic alkali (soda or potash) at a high temperature in a steam 

 boiler, or in cylinders communicating with such boilers. On being 

 heated with caustic soda at a very high temperature, there is formed a 

 thick, jelly-like transparent fluid of pale straw color, which is a hydrat- 

 ed silicate of soda, containing 50 per cent, of water; and which, if 

 exposed to the air for a time, or heated, loses a part of its water and 

 solidifies into a substance capable of scratching glass. 



The history of the silicious stone will now be readily understood. 

 The fluid silicate of soda having been obtained as described above, it 

 is mixed with sand and other material, which may vary according to the 



