660 Transactions of the American Institute. 



euiirJived, and previously coated with a solution containing the fol- 

 lowing ingredients: Plain collodion 8 ounces; nitrate of silver, 100 

 grains; chloride of strotium, 25 grains; citric acid, 20 grains. The 

 coating is rendered permanent by immersing the block into a fixing 

 bath containing a solution of hyposulphite of soda. This pic- 

 ture, however, on the wood cannot be literally followed, as the 

 shading is not made by either line or stipple work. The engraver 

 is not a mere copyist, he must use some skill and judgment in cut- 

 ting his lines so as to produce in the engraving the same degree of 

 shading found iu the photograph. 



NEW BUILDING MATERIAL. 



Mr. F. Ransome, of England, has produced a new stone, by a 

 very simple chemical action, which had not before been made, 

 because, heat and pressure were essential conditions to the reaction. 

 The newly prepared stone is a silicate of lime which contains three 

 elementary substances, namely, calcium, silicon and oxygen. It is 

 the result of the double decomposition of the silicate of soda (water 

 glass) and the chloride of calcium, which form chloride of sodium 

 (common salt) and the silicate of the oxide of calcium (silicate of 

 lime). 



The new material is now manufactured on a large scale, by the 

 Patent Concrete Stone Company, at East Greenwhich, near Lon- 

 don. The silicate of soda is made from a sand of a brownish color, 

 found in great abundance near Maidstone, flints and caustic soda. 

 The flints are heated upon iron gratings within a senis of cylindrical 

 iron dioesters resembling steam boilers. A solution of caustic soda 

 is added, and the digester is closed steam-tight. The mixture is 

 boiled by means of steam, at seventy pounds pressure, carried from 

 a neighboring boiler, through a coil of pipe within the digester. 

 The flint is thus dissolved, forming soluble glass of about 1.2 

 specific gravity; this is drawn off and aftei'ward evaporated until it 

 has a specific gravity of 1.7. 



The sand after being completely diied, by revolving it in a 

 cylinder through which hot air is forced, is mixed with a small por- 

 tion of finely ground carbonate of lime, so as to fill more closely 

 the interstices of the sand. One bushel of this mixture is worked 

 up in a loam mill with one gallon of silicate of soda, forming a 

 sticky substance, which has sufficient coherence to be used in mold- 

 ing like the loam employed by the iron founder. After a mold has 

 been prepared, a solution of chloride of calcium is poured over it, 



