530 PRACTICE OF AGRICULTURE. Part III. 



3402. The criterion of size adopted by M^Adam, is six ounces, or under, for every 

 part of the stratum. 



3403. The size approved of by Clarke is not defined, but it should, he says, be small. 

 ** The common practice is to lay a stratum of stones nearly the size of a man's head, as a 

 foundation, and to cover them with two or three inches of smaller ones ; but, from ex- 

 perience and observation, I am decidedly of opinion, that all the stones should be small, 

 and as nearly as possible of the same size, for though a road made as above described, may 

 be very good at first, the wheels of carriages will grind the small stones to powder, 

 the large ones will then rise to the surface, and the road will become intolerably rough ; 

 and though frequently repaired with new materials the same cause will produce a simi- 

 lar effect ; whereas, if all the stones are small, and nearly of the same size, they will 

 soon be cemented into one solid mass, and will be worn evenly to the last, so that no 

 repairs will ever be necessary, but the addition of a few broken stones occasionally. " ( Obs. 

 on Roads, p. 11.) 



3404. The mode of preparing gravel is nearly the same by all the best road engineers, 

 who agree with Telford, that it ought to be completely cleansed of every particle of clay 

 or earthy substance, and its different sizes ought to be selected and arranged by means 

 of riddling or washing. In the use of the riddle, the particles of earth or clay adhere 

 so much to the stones that it frequently requires to be exposed to the sun, air, and frost 

 for several months, and then riddled over again. In this gravel, the stones are of dif- 

 ferent sizes and different shapes; all those that are round ought to be broken with a 

 small hammer. Some attempt to attain the same end sooner by washing ; but this is 

 both a more expensive, and less effectual mode than that of taking advantage of the 

 weather, 



. 3405. The mode of breaking stones recommended by Edgeworth is by persons sitting, 

 and using small hammers. A hard stone should be used as an anvil, and the stone to 

 be broken may be advatitageously held in a forked stick. Attempts have been made 

 some years ago to break limestone for roads, by the force of horses, wind, and water. 

 Stampers, shod with iron, and raised by proper mill- work, were employed ; they were 

 let to fall upon blocks of whinstones. These mills were found profitable for breaking 

 limestone to powder, as a manure, where fuel was scarce, but they crushed the stone to 

 dust rather than to fragments ; if lighter stampers were employed they frequently failed 

 to break the stone. Feeding the mill was also found difficult and dangerous. This 

 unsuccessful attempt should not discourage mechanics from farther trials. Stones pre- 

 viously broken to the size of five or six inches, might be thrown upon a strong circular 

 horizontal grating, made of cast-iron. The stones might be forced downwards through 

 this grating by an iron rammer on an edge ; they would thus be broken to fragments 

 that could not exceed a certain size, and that would not be reduced to powder. 



3406. The manner of' breaking, according to Telford, is of great importance. More de- 

 pends, he says, on the weight, shape, and manner of using hammers than any one can 

 conceive who has not had much experience in road-making ; the difference in managing 

 this operation being not less than ten per cent. ; and is, besides, of equal importance 

 towards the perfection of the road ; the size and weight of the hammer he would appor- 

 tion to the size and weight of the stones, and the stones should be broken upon the heap, 

 not on the ground. It must be evident that using round stones instead of broken ones, 

 will be the means of deranging the position of those near them, and of grinding them to 

 pieces. 



3407. According to M^Adam the only method of breaking stones both for effect and 

 economy, is by persons sitting ; the stones are to be placed in small heaps, and women, 

 boys, or old men past hard labor, must sit down with small hammers and break them, 

 so as none shall exceed six ounces in weight. 



3408. Breaking by machinery. On a new line of road, between Bury and Bolton, in 

 Lancashire, a rotatory steam-engine is attached to a machine similar to a stone-mill, but 

 considerably stronger, which breaks the stones to cover the road at the astonishing rate 

 of seventy or eighty tons in ten hours. The engine is moveable on wheels, so that it 

 can be removed to any part of the road without being taken to pieces. (London Journal 

 of the Arts, ^c. Sept. 1822.) 



3409. M* Adam's criterion for size is weight. On being asked by the road com- 

 missioners to mention the dimensions, he stated, that there was very little difference in 

 the weight of the stones used in road-making. " I did imagine," he says, ** that a dif- 

 ference existed, but having weighed six ounces of diflerent substances, I am confident 

 there is little difference in appearance and none in effect ; I think that none ought to 

 exceed six ounces ; I hold six ounces to be the maximum size. If you made the road 

 of all six-ounce stones it would be a rough road ; but it is impossible but that the greater 

 part of the stones must be made under that size." * Do you find ^ measure or ring through 

 which the stones will pass, a good method of regulating their size ?' " That is a very 



