136 Miscellaneous Intelligence, 



mortar, he obtained some so hard, as to b^ capable of cutting a 

 ruby, when employed instead of diamond-dust. 



Mr. Gill by grinding Greek emery-stone between two flat and 

 hard steel surfaces, and washing off the lighter portions in oil, 

 found that those which subsided in half a minute, when examined 

 by a microscope, had entirely resisted the friction, and were per- 

 fectly crystallized sapphires. — Tech. Rep, vii 45. 



6. Power of Building Materials to resist Frost. — In the xvii. vo- 

 lume of this Journal, p. 148, we gave an account of a process devised 

 by M. Brard, for the estimation of the power possessed by building 

 materials, of resisting the disintegrating action of frost and 

 weather. He imitated this action by the spontaneous crystal- 

 lization of a solution of Glauber's salt, the crystals producing the 

 same effect upon the particles of the stones submitted to trial as 

 the formation of ice would have done by the exposure of the same' 

 stone to cold after being moistened. The importance of M. 

 Brard's process, and its great utility to architects, has been proved 

 in France by MJVI. Vicat, Billoudel, Conrad, and de Thury, who 

 in consequence consider the means as known, by which the power 

 of any building-stone or material to resist the disintegrating action 

 of frost or weather, may be ascertained in a few days. 



In addition to the directions formerly given, the following 

 have been added in the instructions drawn up by the French 

 philosophers. The stone having been selected, the cubes cut, 

 and the solution of sulphate of soda (saturated at common tem- 

 perature) made, the solution is to be boiled, and whilst boiling 

 freely, the specimens are to be introduced. The stones are to be 

 boiled for half an hour and not longer : M. Vicat having shewn 

 that afterwards the effect surpasses that of frost. The specimens 

 are then to be withdrawn one after the other, and suspended by 

 threads, so that they do not touch each other, or any thing but the 

 thread ; a vessel containing some of the clean solution in which 

 they have been boiled is to be placed beneath each, after which 

 the vessel and its accompanying specimen are not to be 

 separated. 



If the weather be not too moist or too cold, the specimens will be 

 found covered in 24 hours with small white saline needles. They 

 are then to be-plunged, each into the particular portion of solu- 

 tion beneath it, when the needles fall off, and are again to be sus- 

 pended in the air. A repetition of this process is to take place 

 each time the needles are well formed. If the stone under trial is 

 capable of resisting the action of frost, tlie salt will remove 

 nothing from it, and neither grains, nor scales, nor fragments, will 

 be found at the bottom of the solution beneath. On the con- 

 trary, with a stone which gives way to the weather, it will be seen 

 that even on the first day the salt will remove particles from it, 



