48 ANNUAL OF SCIENTIFIC DISCOVERY. 



succeeded in preparing the so-called water-glass, an alkaline solu- 

 tion of silica in water, we will shortly glance over what has been 

 done during the past ten years. It was at first believed that the 

 German water-glass would answer all the purposes above stated ; 

 however, it was soon found that the carbonic acid of the atmos- 

 phere, by its stronger chemical affinity for the alkali of the sili- 

 cate, caused a gradual disintegration of the surface or compound. 

 Numerous remedies were suggested to counteract this evil. 

 Prof. Kuhlman, in Lille, France, and Mr. Ransome, in Ipswich, 

 England, partially succeeded, by subsequent application of the 

 solutions of chloride of calcium and hydrofluoric acid to the sur- 

 face, or to the mass of the stones, to neutralize and extract the 

 alkali ; and Mr. Ransome, by the means of great pressure and 

 proper manipulation, is preparing a concrete stone of considera- 

 ble hardness and durability. 



Prof. Graham, in London, by his beautiful discovery of dialysis, 

 by which a cry stalliz able liquid can be separated from a viscous, 

 or so-called colloid substance, first succeeded in separating silica 

 from an alkaline silicate, and in keeping it in perfect solution in 

 water. However, the slowness of the process, and the small 

 quantity of silica thus kept in solution, left this very ingenious 

 and otherwise useful method without practical results. It is only 

 recently since the eminent French chemist, Fremy, has made a 

 thorough scientific investigation into the nature and properties of 

 silicium and its combinations with chlorine, fluorine, and sulphur 

 that the existence of several distinct hydrates of silica has be- 

 come known. 



In this country, Mr. Benj. Hardinge, of New York, some twelve 

 years since prepared, by a peculiar process not made public, a so- 

 lution of silica in water, wherein the silica was largely in excess ; 

 and recently he has succeeded in producing not only a most per- 

 fect imitation of white and colored statuary marble, but also in 

 making a snow-white flint of greater hardness and durability than 

 the natural marble itself. He succeeded in mixing his compounds 

 so that the exact amount of water of crystallization necessary for 

 the formation of the stone was introduced, and the stone, cast 

 cold, without pressure, becomes hard from the centre outward ; 

 thus insuring durability and compactness. This is a great step 

 toward the solution of our problem. A new process has very 

 recently been invented, by which a soluble hydrate of silica, en- 

 tirely free from alkali or any other matter, can be prepared 

 cheaply and on a large scale from sulphide of silicium. 



NEW CEMENT AND BUILDING MATERIAL. 



In a communication to the French Academy in July, 1867, M. 

 Sorel describes a new cement, a basic hydrated oxychloride of 

 magnesium, obtained by slacking magnesia with a solution of 

 chloride of magnesium in a more or less concentrated state. The 

 denser the solution the harder it becomes on drying. This mag- 

 nesium cement is the whitest and hardest of all known to this day, 

 and can be moulded like plaster, in which case the cast acquires 



