132 THE BOULEVARDS . 



When thorouglily melted — wliich may be told by tbe mastic 

 dropping freely off the stirrer^ and by jets of light smoke 

 darting out of the mixture — ^it is conveyed quickly to the 

 spot where it is to be used;, in heated iron buckets or 

 ladles. The cauldron ought to be as close to the work as 

 possible, and in covering brick arches it should be hoisted 

 to the top of the building. It must be clearly understood 

 that the only kind of bitumen to be used is that impreg- 

 nating the limestone itself. 



In forming foot or carriage ways it is most important to 

 secure a good foundation by removing or ramming the soft 

 earth;, and laying a course of concrete^ care being taken to 

 allow the whole to dry before putting down the asphalte. 

 If this precaution is not attended to, the heat will convert 

 the moisture in the concrete into steam, and fill the asphalte 

 full of airholes and bubbles. The thickness of the layer of 

 asphalte may be regulated by slips of wood arranged across 

 the pavement at a distance of 30 inches from each other — a 

 width quite sufficient for one man to work at at a time. If 

 two men are employed, double the width may be taken, as 

 it is always better to have as few joints as possible. The 

 work is levelled with a long curved wooden spatula, assisted 

 by a long straight ruler, which stretches across the layer of 

 asphalte, over which it is moved backwards and forwards, 

 the wooden gauges supporting its ends. If the surface is 

 intended to be smooth, a mixture of equal parts of silver 

 sand and slate dust or plaster of Paris is sifted over it before 

 it has quite set, and rubbed down with a flat tool of wood. 

 If it is required to be rough, sharp grit is to be beaten in 

 with a heavy wooden block. One portion of the pavement 

 being complete, it is best to proceed to lay the next but 

 one, leaving the intermediate space to be filled up after- 

 wards, when the first layer is firm and cold, so as to insure 

 a good joint. 



The thickness of asphalte for footways varies from 

 half an inch to an inch and a quarter, the former being 

 sufficient for common floors and courtyards, the latter for 

 carriage pavements. A thickness of from half an inch to 

 five-eighths is sufficient for roofs and the coverings of arches, 



