K. MECHANICS AND ENGINEERING. 409 



six inches, laying the roadway with them, and then covering 

 the whole with fragments, broken to about two inches in 

 size, to a depth of about four inches (making ten inches in 

 all), after which the road is to be well watered, and crushed 

 with a heavy roller. In this way an almost solid bed is 

 made, which is entirely free from mud, almost- so from dust, 

 and of uncommon durability. Indeed, this method seems to 

 have given so much satisfaction lately in England that prep- 

 arations are being made to use it for paving certain portions 

 of London, with the anticipation that it will answer much 

 better than the asphaltum rock heretofore imported from 

 France, and applied there to a similar purpose. 8 A 9 March 

 1,50. 



ARTIFICIAL PORPHYRY. 



Messrs. Sepulchre and Ohresser have lately published an 

 account of a method of treating furnace sla^ so as to obtain 

 a kind of artificial porphyry scarcely inferior in durability or 

 strength to the natural substance. For this purpose they dig 

 furrows in the slag pit having the shape of an inverted trun- 

 cated cone, and from twelve to fifteen feet wide, so as to 

 receive the entire amount of slag produced in one or more 

 furnaces at any one drawing off. The melted slag is to be 

 emptied in this by means of suitable channels, and the cavity 

 can be divided up by partitions, so as to cast the mass either 

 in one continuous block, or in a number of blocks of any giv- 

 en shape. Care must be taken to have the slag run under 

 the thickened glassy covering which forms at the beginning 

 of the operation, the object of such a coating being to retain 

 the heat ; and it is even necessary sometimes to protect the 

 mass against too rapid cooling by a covering of ashes, as this 

 cooling should occupy several days, varying with the amount 

 of the slag. When the operation is completed a dense homo- 

 geneous block or blocks will be found underneath this glassy 

 covering of the character of natural porphyry, as stated. 



This material has been tested by suitable methods, and has 

 been found to bear a pressure of about 700 pounds to the cu- 

 bic centimetre (a cube of about four tenths of an inch), while 

 for complete crushing a pressure of about 1100 pounds was 

 required. In other experiments with this artificial stone, 

 fracture never occurred under a pressure of less than 600 



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