SILICEOUS CEMENTS 783 



a deposit of this kind contains 77'05 of silicic acid. The hot springs of New Zealand 

 deposit a crust containing 75 of silica ; and some springs in the Azores leave precipi- 

 tated a stratum containing 67~6 of silica. In the Steamboat Springs in California 

 remarkable deposits of silica, associated with metallic sulphides, are in course of 

 formation. 



The Dinas sand, Glamorganshire, is remarkable. Some samples are actually pure 

 silica, and most of it gives 91'95 of silicic acid: the sand of Penderyn, in the same 

 county, giving 94'05 silica. A similar deposit is found near Llandudno, in North 

 Wales. See STONE, ARTIFICIAL. 



SILICATE PAINTS. Curious local deposits of almost pure silica have been 

 discovered near Llandudno, in North Wales. The deposit lies in a basin, at a con- 

 siderable level aboA'e the sea, and appears to form the bed of a small lake. The 

 silica bod has a thickness of several feet, and overlies a deposit of greater thickness, 

 but less purity. Tho following analysis has been made thereof : Silica, 79 parts ; 

 water, 13 ; oxide of iron, 3 ; alumina, 4; magnesia, 1. 



This material is unique, and possesses a wide range of usefulness in tho arts and 

 manufactures. It would be especially suited for producing crystal glass, and in the 

 manufacture of porcelain, if the small percentage of. oxide of iron were removed from 

 it. Again, chemists report that this earth is a peculiar and interesting material, and 

 is almost pure silica thoroughly calcined, reduced to such an impalpable powder as to 

 be, without further treatment, fit to be employed in various ways. 



The material, when excavated, is freely washed in water, which holds it in partial 

 suspension, and is then allowed to dry, when it becomes brilliantly white, and is more 

 finely divided than could be done by mechanical means. At present the use made 

 thereof is in the production of paint. Before being so used the water is dried out, so 

 that the base of the paint contains 92 per cent, of pure silica. For this purpose it is 

 especially suitable, as it mixes freely with the pigments and oils, and is worked with 

 the greatest ease. Moreover, it entirely resists the action of acid, and the effect 

 of heat, and, when laid on, becomes extremely hard and polished on the surface ; no 

 small advantages. 



The Silicate Paint Company (Fenwick Street, Liverpool), supply this itseful paint. 

 Its preservative influence, in shielding sensitive materials from the destructive action 

 of heat and flame in conflagrations is insisted on, but surely a mere coating of silica 

 cannot possess any extraordinary power in this respect. 



The Silicate Paint Company also manufacture a water-proofing solution from this 

 peculiar silica, which, when applied to the interior or exterior of houses, entirely ex- 

 cludes damp. The silica is conveyed into the pores of the brick, plaster, stone, or 

 other material, and the action of the air causes it to petrify and return to its original 

 condition. See STONE, ARTIFICIAL. 



SZIiICATIS ATION. The process of impregnating bodies with silica. 



SILICATES. Compounds of silicic acid (silica, oxide of silicon or silicium), with 

 earthy, alkaline, or metallic bases. In mineralogical arrangements these have been 

 divided into anhydrous silicates, which include, as Dana classifies them, tho augite 

 section, the garnet section, the mica section, the felspar section, and some others ; and 

 the hydrous silicates, which include the talc section, the serpentine section, the chlorite 

 section, the calamine section, the datholite, and others. 



SILICEOUS CEMENTS. An interesting paper on hydraulic cements was 

 submitted to the Academy of Sciences by M. F. Kuhlmann, showing the advantage 

 that may be derived from the combination of silicates with mortars and cements in 

 general, and especially with those that are intended to resist the action of sea-water. 

 It is well known that the first effect of water on cements is that of forming hydrates ; 

 after which a gradual contraction takes place, producing a degree of hardness, which 

 increases in proportion as the contraction is slower, and there is more silex or alumina 

 in the cement. Now, M. Kuhlmann has observed that if alumina or its silicate, or else 

 magnesia, whether caustic or carbonated, be kneaded into a paste with a solution of 

 silicate of potash or soda, the compounds resulting therefrom will bear a perfect resem- 

 blance to the natural silicates, such as felspar, talcose slate, magnesite, &c., and will, 

 by repose and slow contraction, become hard and semi-transparent, resisting in a high 

 degree the erosive effects of water. If slaked lime be added to the said compounds 

 they acquire the properties of hydraulic cements. M. Vicat, junr., having shown that 

 calcined magnesia added to a cement would resist tho action of sulphate of magnesia, 

 M. Kuhlmann endeavoured to turn this observation to account, by mixing cal- 

 cined dolomites (which contain magnesia) with mortar, containing the alkaline 

 silicates. This composition he found very advantageous, since most of the salts con- 

 tained in sea-water must contribute towards the preservation of such cements. In 

 fact, the chloride of magnesium, as well as the sulphate of magnesia, will be decom- 

 posed and form a layer of silicate of magnesia on the surface of the cement ; in the 



