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POPULAR SCIENCE MONTHLY 



sand and water to the consistency of mortar and used. Like natural 

 cement, Portland cements are hydraulic, and they make the strongest 

 mortars known. 



A modern street consists of a foundation of broken stone that is 

 formed into a concrete or solid mass of masonry by admixture with 

 mortar. The character and quality of this mortar are a matter of the 

 greatest importance. All of the four kinds of mortar mentioned above 

 have been used for this purpose. 



An experiment was made in London by laying in Holborn, opposite 

 Gray's Inn, nine inches of lime mortar concrete with a floating on top 

 of % inches of lime mortar. Upon this foundation was laid a surface 

 of Val de Travers asphalte. When the concrete was ready to receive the 



Fig. 1. Coal Du.mi'.s and Inclines to Kilns. 



asphalte, a fire broke out in Holborn ; the place was flooded with water, 

 the engines drove over the concrete and the population of Gray's Inn 

 trampled it down. It was subsequently made good and the asphalte 

 spread. Tor five or six years the road was kept up at considerable ex- 

 pense and then relaid. On removing the asphalte, it was found that 

 the lime concrete had never set, that the mortar floating had never 

 adhered to the concrete, but was mostly in powder, produced either Jby 

 the action of the rammers or by the trafiic afterwards. 



Eoman cement was tried in Paris and condemned for street 

 foundations. There remains for use for this purpose natural cement 



