Chap. IX.] AVENUES AND BOULEVARDS. 147 



after having heated the two sides of the boiler, passes out by a 

 chimney placed at the back of the machine. Means to keep the 

 mastic in motion, and prevent its burning by adhering to the 

 sides of the boiler, are secured by a simple mechanism easily 

 worked by the hand. These carriage boilers, full of liquid 

 asphalte, are driven from place to place with the greatest facility. 

 The boiler is emptied by the means of a pipe fixed to its bottom, 

 and the mastic is collected in a pail, and spread on the surface to 

 the thickness of three-quarters of an inch. 



If the surface is not perfectly dry, the drying must be ac- 

 celerated with hot ashes, which are to be taken away afterwards, 

 or with a little spreading of quicklime in powder. These opera- 

 tions are indispensable, as if the mastic were laid on before the 

 surface is dry, the heat of it would dispel in steam the water 

 underneath, and that steam would produce blisters in the asphalte 

 which would crack under the pressure of the feet, and • endanger 

 the success of the operation. The workmen place on the platform 

 two iron bars of the same thickness as the asphalte is to be, 

 at equal distance from each other ; it is then laid down in a very 

 warm state, and thick enough to require some slight exertion of 

 the operator to make it level. This done, a small quantity of fine 

 gravel must be spread over the asphalte while hot, and slightly 

 beaten down to penetrate into it. This gives a greater hardness 

 and solidity to the footway, and insures its lasting for a very 

 long time. 



The roads before spoken of are made of the powdered and not 

 liquid asphalte. The surface of the roadway must be beaten down 

 very hard, and covered with a thickness of about three inches of 

 concrete, well beaten down and dry. If the dryness is very 

 necessary in the making of a pavement, this condition is of a 

 greater importance for the road, as, if the powder were spread on 

 a wet surface, the steam caused by the heat would produce a great 

 number of little fissures, the elasticity would be destroyed, and 

 the road would be useless after a few months' use. The concrete 

 well dried, the powder (hot) must be spread about three inches 

 thick; and then well levelled and beaten. The sides must be 

 done first, and pressed down with a rectangular iron pestle eight 

 or nine inches in length and two or two and a half inches in 

 width When the sides are done, the middle is proceeded with 



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