38 HYDROPLASTICS. [H. 



foot-pavements in Philadelpliia have not been very successful ; 

 probably owing to want of experience in those who constructed 

 them, or possibly to some defect in the composition. In some 

 instances, the asphalt covering is worn through in the course 

 of a few years ; in others, especially where exposed to the 

 almost constant action of the summer's sun, the asphalt, be- 

 coming slightly softened, has been gradually pushed down the 

 slope of the pavement, and appeared like a cascade of lava 

 falling over the curbstone. An experiment made by J. C. 

 Cresson, at the Philadelphia gas-works, some years since, with 

 coal tar boiled down to pitch and thickened with sand, seemed 

 to promise success. It was spread on a wooden floor, exposed 

 to the weather and traversed frequently by carts, and yet 

 showed few signs of complete abrasion, although subjected to 

 so trying a test. 



A Steam Cement. — An English cement of this kind, ana- 

 lyzed by Yarrentrapp, consisted of 2 pts. litlmrge, 1 pt. fine 

 sand, and 1 pt. fallen lime. After mixing the powder with 

 oil or varnish, it should be used at once, as it soon becomes 

 hard. It is used for stopping up joints in steam-engines. 



