68 ANNUAL OF SCIENTIFIC DISCOVERY. 



and chips of stone, we add about 1 part of calcined magrnesia, 

 and mix them toorether, with sufficient bittern water to I'orm a 

 stiff mortar, which mortar may be moulded and pressed, or simply 

 moulded, or applied with a trowel. 



'* Heat may be used to hasten the hardening process ; but this 

 is not generally necessivrj% as the stone dries well in the open air, 

 and indurates perfectly in 2 or 3 weeks, without an}^ ajDplication 

 of artificial heat. 



" By this process, sand, soapstone, marble, or other mineral 

 substances, in broken, pulverized, and comminuted form, may be 

 used for the production of blocks and slabs, the invention being 

 particularly valuable for the utilization of chips in stone quarries, 

 and of marble, soap-stone, and slate-stone dust and chips, in 

 places where these minerals are worked. The stone so made 

 answers perfectly for building purposes, for tiles, for stone sinks, 

 stoves, etc., and, generally, the same purposes for which bricks, 

 clay, and stone blocks and slabs are emploj'ed. 



" The relative quantities of finely pulverized and of broken 

 materials that are used depend somewhat upon the size of blocks 

 that are to be formed ; but it is only necessarj' for the producing 

 of the stone that the mortar, made up of the jDulverized stone and 

 the calcined magnesia and bittern water, should till all the inter- 

 stices and spaces between the broken stones or chips." 



PRESERVATION OF BUILDING STONE. 



An Illinois architect has invented a process for preserving from 

 decay and disfigurement the beautifully colored stone called 

 *' Athens marble," which is now used very extensively at the 

 West for building fronts. This stone is composed principall}^ of 

 carbonate of lime, carbonate of magnesia, and silica, but among 

 the minor ingredients, protoxide of iron pervades the whole mass, 

 giving the characteristic blue-greenish tint, the main cause of its 

 beauty, but the cause also of its decay, as exposure to the atmos- 

 phere converts the protoxide into hydrated sesquioxide of iron, or 

 iron rust. To remedy this action the stone is coated with a solu- 

 ble glass, made by melting a mixture of 15 parts of silica, 10 of 

 soda, and 1 of charcoal, until it forms a glass which is reduced to 

 the liquid form by boiling in water. This solution permanently 

 fastens itself to the surface and protects the stone from the atmos- 

 phere, smoke, and dust. — Scientific American. 



LARGE ROOF. 



The metropolitan station now being erected for the Midland 

 Railway at King's Cross, London, is nearly as great an advance in 

 the construction of roofs as the Great Eastern was in the building 

 of ships. Tiie new building is erected alongside of the Great 

 Korthern Station, which was a short time since regarded as a 

 tremendous structure. Some idea of the advance made of late 



