The smaller the stone is broken the heavier a cubic yard of it will weigh, as the percentage of vacant space between each stone will be less. It has been found by experiment, however, that 55 per cent. of ordinary road metal is solid, so that the weight of a cubic yard of it can easily be ascertained in the following manner.[41]
Multiply the weight of a cubic foot of any stone by 27 to bring it to a cubic yard, and then multiply this by 0·55: the result will be the weight of a cubic yard of the same stone when broken for metalling.
A cubic yard of Guernsey granite broken to pass through a 2¹⁄₂ inch ring has been weighed, and gives an average of 1 ton 3 cwt. 2 qrs.
| tons | cwt. | qrs. | |||
|---|---|---|---|---|---|
| A cube | yard of | flint weighed | 1 | 1 | 3 |
| „ | „ | pit gravel weighed | 1 | 4 | 3 |
| „ | „ | limestone weighed | 1 | 3 | 0 |
A cubic yard of ordinary broken road metal will, when properly spread, cover an area of about 30 square yards of surface of a roadway.
The following specimen specification for the supply of stone either unbroken or broken may be of use.
Specification for the Supply of Road Metal.
(1.) The road metal must at all times be clean and free from clay or other dirt, and fully equal to the sample; if required to be broken, each cube must have a square face and sharp edges, and pass all ways through a 2¹⁄₂ inch ring.
(2.) The metal must be delivered in (name of town) free of all charge to the corporation, either at a railway station or at one of the depôts of the corporation, at the option of the contractor, such option to be declared in the tender.
(3.) The metal must be supplied on the order of the borough engineer in such quantities as he may specify, and must be delivered within the time specified in the order. The contractor shall not be required to supply and deliver more than tons in any one week; but the corporation will be at all times ready to take the metal in larger quantities.