K. MECHANICS AND ENGINEERING. 407 



VICTORIA STONE. 



A new artificial stone, known as Victoria stone, is now be- 

 ing manufactured in England by a process perfected by Mr. 

 Highton. This consists in mixing broken granite, the refuse 

 of granite quarries, with hydraulic cement, and steeping the 

 mass in silicate of soda. For this purpose the concrete mass- 

 es to be silicified are immersed in a tank of silicate of soda, 

 in which are placed pieces of a peculiar silicious stone ob- 

 tained at Farnham, possessing the property of having its sili- 

 ca in such a state as to dissolve in cold caustic soda. The 

 lime of the concrete mass takes silica from the silicate, and 

 the soda set free redissolves silica from the Farnham stone. 

 Hence the process is continuous. 5 A, July^ 1870, 317. 



PORTLAND CEMENT. 



According to recent extensive experiments, it appears that 

 a sewer constructed of concrete composed of one part cement 

 and six parts sand, and lined inside with cement, is the cheap- 

 est form of sewer, combining strength with soundness. The 

 experiments also proved that the strength of Portland ce- 

 ment increases with its specific gravity, its more perfect pul- 

 verization, and its thorough admixture with the minimum 

 quantity of water in forming mortar. Heavy and pure ce- 

 ment, weighing 123 pounds to the bushel, it is stated, will 

 take about two years to attain its maximum of strength, and 

 the admixture of sand or gravel reduces the strength of the 

 concrete, which sets less rapidly than the pure article. Ro- 

 man cement, though setting quickly, deteriorates in strength 

 after exposure to air before use about twice as much as Port- 

 land cement. 



HARD CEMENT. 



A cement which becomes excessively hard in time may be 

 prepared by mixing two parts of silica, one part of silicate of 

 alumina, and nine or ten parts of carbonate of lime, all in 

 powder, and then roasting in a puddling furnace. The re- 

 maining mass is then to be ground and again roasted with 

 two or three parts of carbonate of baryta. In practice, very 

 pure sand will answer for the silica and chalk for the carbon- 

 ate of lime, the remaining ingredient being supplied by min- 



