Polytechnic Association. 773 



in uniting inert bodies, as lime, and that would not bear a large admix- 

 ture of sand. 



The speaker said that he had deemed the previous observations 

 necessary, in order to show that the mere fact of Sorel's using oxide 

 of magnesium in his cement, was not sufficient to account for its great 

 strength ; and, furthermore, that it was not because " certain hydraulic 

 limestones owe their hardness and power of setting under water to 

 magnesia," or " because geologists agree that some of nature's most 

 indestructible rocks contain that substance." He alluded to the fact 

 that talc also contains magnesia, and yet that it is the softest of all 

 minerals. 



The process of making the Sorel artificial stone was then minutely 

 described. It was divided into four different operations : 



1st. The preparation of the oxide of magnesium. 



2d. The mixing of sand Math inert materials. 



3d. The mixing of the afore-mentioned materials with chloride of 

 magnesium. 



4th. The moulding of the resulting mixture. 



These operations were described as carried out by the Union Stone 

 Company, in Boston, the owners of Sorel's patent for the United 

 States. 



Strength. 



From experiments made by Major-Gen. Gillmore (vide his Practical 

 Treatise on Coignet-Beton and other Artificial Stone, New York, 

 1871), it follows that in strength and hardness, the Sorel artificial 

 stone surpasses all other known artificial stones and is, equaled by 

 few, if any, of the natural stones adapted to building purposes. 



The following figures express the crushing pressure per scpiare inch 

 in pounds. 



Natural Stones. 



Granite, Quincy 15 > 300 



Marble, Montgomery county, Tenn 8 j 950 



Sandstone, strong 5 5 500 



Granite, Patapsco 5 j 340 



Sandstone, Connecticut 3 » 319 



Artificial Stones. 



Sorel, Union Stone Company, Boston 21 > 562 



Sorel, Union Stone Company, Boston, magnesia by weight 



fifteen per cent, inert material : fine marble 11? 556 



Sorel, Union Stone Company, Boston, magnesia by weight? 



inert material : marble with colored veneer 7? 680 



