CHEMICAL SCIENCE. 263 



powder for optical glasses, metals, etc. At the present price of sulphate of 

 iron and oxalic acid, it may be prepared for about five shillings per pound. 

 Buchner's News Report. 



ON HYDRAULIC LIME, ARTIFICIAL STONES, AND SOME NEW 

 APPLICATIONS OF THE SOLUBLE ALKALINE SILICATES. 



M. Kuhlmann, in a recent communication to the French Academy presented 

 some interesting facts respecting the hydraulic limes, artificial stones, etc. His 

 examinations show that all limestones, especially the hydraulic limes and nat- 

 ural cements, contain notable quantities of potash and soda. The part which 

 these alkalies serve, is to bring the silica to the lime, forming silicates which, 

 in contact with water, pass into a state of hydratation similar to that of gyp- 

 sum. A fat lime may be immediately transformed into an hydraulic lime by 

 simple contact with a solution of silicate of potash. If after the burning of 

 the limestone, potash be in contact with the silica, the silicate which is formed 

 must necessarily react ; but this can not occur until the lime is brought into 

 contact with water. If fat lime and an alkaline silicate, both in fine 

 powder, be mixed in the proportion of ten or twelve of the silicates to 100 

 of lime, a lime can be obtained which presents all the characters of an hy- 

 draulic lime. If the ingredients were not finely powdered the reaction would 

 be incomplete, and after the solidification, a disintegration of the mass would 

 take place. This affords the means of constructing, at moderate expense, 

 buildings to resist the action of water, where none but fat limes are found. 

 By mixing powdered chalk with a solution of silicate of potash, a cement is 

 obtained which hardens slowly in the air, and becomes sufficiently hard to be 

 applicable under certain circumstances, for the restoration of public monu- 

 ments, the manufacture of molded objects, etc., etc. Chalk, whether in an ar- 

 tificial paste, or in its natural state, if plunged into a solution of silicate of 

 potash, absorbs even in the cold, a quantity of silica^ which may be increased 

 to a considerable extent by exposing of the stone alternately, and for many 

 times to the action of the solution and of air. The chalk assumes a smooth 

 appearance, a compact grain, and more or less of a yellowish color, according 

 as it is more or less impregnated with iron. Stones thus prepared are sus- 

 ceptible of receiving a high polish. The hardness which at first is but super- 

 ficial, penetrates by degrees into the center, even when the stones are of con- 

 siderable thickness. They appear susceptible of undoubted utility in the 

 formation of works of sculpture and various ornaments, even those of the 

 most delicate workmanship ; for where the silicatization has been effected on 

 well-dried chalk, which is essential for the production of the best results, the 

 surface remains unaltered. Some attempts have been made to apply these 

 stones for lithography which promise success. 



This method of converting soft limestone into silicious limestone may 

 become of great value in the art of building. Ornaments unaffected by damp 

 and of great hardness may thus be obtained at little cost, and in many cases 

 a plaster made with a solution of silicate of potash will preserve from decay 

 ancient monuments formed of soft limestone. 



