The following table of the proportions necessary for the bituminous mixture may here be of use.
Proportions for Bituminous Mixture.[64]
| Pitch. | Tar. | Pitch. | Creo- sote oil. | |||||||
|---|---|---|---|---|---|---|---|---|---|---|
| For grouting in pavements | 1 | to | 1 | or | 3 | to | 1 | |||
| For foundations or lower layer of asphalte macadam | 3 | to | 1 | or | 3 | ¹⁄₂ | to | ¹⁄₂ | ||
| For upper layer of asphalte macadam and for foot paths | 2 | ¹⁄₂ | to | 1 | ¹⁄₂ | or | 3 | ¹⁄₄ | to | ³⁄₄ |
The objections to this method of paving are only temporary: the nuisance arising from the fumes of the boiling mixture whilst it is being applied, and the necessity for dry weather to make the operation successful. Healey’s Patent Pitch Boilers[65] are said to moderate, if not entirely to do away with the former, and the latter can be arranged by only doing the work at favourable seasons, or if the worst come to the worst, to cover the work with tarpaulins raised on trestles.
Before closing this chapter I should like to draw attention to the question of provision for wheel tracks, or tramways paved with stone, asphalte, or other hard material, and a track for horses giving a firmer foot-hold, similar to those so highly spoken of in Milan and other Italian cities. An excellent description is given of them by Mr. P. le Neve Foster, Jun., in an appendix to a report on the Application of Science and Art to Street Paving and Street Cleansing of the Metropolis (1872).
The roadway where stone tramways are employed cannot be of convex section; on the contrary, it should be concave, with the channel, gutter, or water table in the centre. This is in itself an obvious advantage, and I trust that the question of these tramways may at some future date receive more attention from English engineers; the great objection to them in this country being that the smooth tram-track would be very slippery and apt to throw horses down when passing on and off, but they have many advantages which should not be passed over without consideration.[66]
[53] Birmingham in 1854 had not, I believe, a single mile of paved streets; the principal ones are now nearly all paved with granite setts, and over 20,000 square yards were so paved in 1880.
[54] It is said that the cost per annum per square yard of granite paved roadways is but 3d., whereas the same cost for macadamised roadways under the same circumstances is 1s. 6d.
[55] In Paris after considerable research into the question, the engineers of the Ponts et Chausseés, decided that the size of the paving stones, which used formerly to be 9 inches square should be 4 inches wide by 6¹⁄₄ inches long by 6¹⁄₄ inches deep, the stone that is used being a grit sandstone, from the forest of Fontainebleu.