Page:Historic highways of America (Volume 15).djvu/159

 water, and a cubic yard of broken macadam will weigh just about one-half as much as a solid cubic yard of the same kind of stone. Isaac Potter says:

"To insure a solid roadway and to fill the large proportion of voids or interstices between the different pieces of broken stone, some finer material must be introduced into the structure of the roadway, and this material is usually called a binder, or by some roadmakers a 'filler.'

"There used to be much contention regarding the use of binding material in the making of a macadam road, but it is now conceded by nearly all practical and experienced roadmakers, both in Europe and America, that the use of a binding material is essential to the proper construction of a good macadam road. It adds to its solidity, insures tightness by closing all of the spaces between the loose, irregular stones, and binds together the macadam crust in a way that gives it firmness, elasticity, and durability."

Binding material to produce the best results should be equal in hardness and toughness with the road stone; the best