38 ANNUAL OF SCIENTIFIC DISCOVERY. 



By tlie insertion of suitable cores, holes for the insertion of the 

 joists, or for other puriJoses, may be moulded in the concrete as 

 the work proceeds. 



LIME CONCRETE IN CONSTRUCTIONS. 



Mr. F. Ingle conimunioatod to the British Association, in 1806, 

 a ]Kiper in which he pointed out what he considered a radical 

 defect of concrete formed from lime as ordinarily used, viz., that 

 by the action of fire it becomes reconverted into lime, which, 

 when the water from the engines is brought to bear ui)on it, 

 expantls greatly, and forces out the walls, to the destruction of 

 the Ijuildiiig. lie advocated the use of a concrete formed from 

 g}'2^^"'i'> wliich is not liable to this defect. The gypsum, which 

 is of a coarse and inexpensive character, is formed into j)lasti'r of 

 Paris by roasting, and mixed with a pecuhar kind of clay found 

 in counection with the beds of gypsum. 



HYDRAULIC CEMENTS. 



M. Fremy communicated, in May, 1805, an important paper on 

 this subject to the French Academj' of Sciences. Vicat assumed 

 the formation of a douljle-silieate of alumina and lime, wliich, by 

 absorbing water, was the cause of the setting of hydrauHc ce- 

 ments, and this view seemed to be confirmed by finding in the 

 calcined cements a silicate which formed a gelatinous precipitate 

 witli an acid, whicli silicate did not pre-exist in tin; stone before 

 calcination. MM. llivot and Chatonay suggested that the calci- 

 nation of the argillaceous limestone gave rise to an aluminate of 

 lime having the formula Al- O" 3 Ca O, and to a silicate of lime 

 represented by Si O-^ 3 Ca O, which salts brought into contact 

 with water form hydrates, each with six equivalents of water, and 

 thus cause the setting. 



The result of the experiments of M. Fremy is, that the setting 

 of cements is due to two difi'erent chemical actions : first, to the 

 hydration of the aluminates of lime ; and secondly, to a puzzu- 

 olanic action, in which the hydrates of lime combine with the 

 silicates of lime and alumina. He found that alumina is even a 

 better flux for lime than silica, and he suggests that the very 

 basic compoiuids of these two substances — those, for instance, 

 containing from 80 to 90 per cent, of lime — may be useful in the 

 iron furnace, owing to their disposition to absorb sulphur and 

 phosphorus, and thus free the metal from these noxious impuri- 

 ties. He also finds that no substance is capable of acting as a 

 puzzuolana except the simple or double silicates of lime, con- 

 taining only from 30 to 40 per cent, of silica, and sufficiently 

 basic to form a gelatinous precipitate with acid. 



INSOLUBLE SILICATE. 



M. Ch. Guerin called the attention of the French Academy to 

 a new method of obtaining, by a cold process, a silicate com- 

 pletel}' insoluble, which can be ajjplied either as an external coat- 

 ing, as in the case of glass or iron, or made to penetrate throui^h 

 the interior of the substance, as for the preservation of wood and 



