656 PROCEEDINGS OF SECTION H. 



out to SO treat the macadam surface that any dust formed or grit worn 

 off would be made self-binding and reinforce the surface like a mat 

 or cushion. In this way the life of the road might be greatly increased 

 and the comfort of the people equally improved by lessening the vibra- 

 tion, noise, and dust. Others, again, have attacked the problem from 

 another direction, and have sought to combine with the macadam some 

 substance which will virtually produce a new kind of pavement, or 

 substitute a new and different pavement altogether, having the desired 

 qualities in a high degree. 



Following up the latter scheme first, it will be seen that such pave- 

 ments include mineral asphalte, wood blocks, and others which are 

 too costly for the majority of the streets. Tar pavements of various 

 kinds have been tried with more or less success for a time, but they are 

 difhcidt to repair and are extremely hot — in fact the hottest pavement 

 known. When double-distilled tar is used and the traffic is not heavy 

 they give good results, though more costly than tar-dressed roads, 

 and their use is chiefly indicated when the traffic is too heavy for the 

 latter. All pavements which are of the nature of a substitution have 

 this great drawback, that they can only be adopted as existing pave- 

 ments become worn out, and relatively they are costly, and, with the 

 exception of Val de Travers asphalte, require frequent dressings of tar 

 and sand, estimated at 2d. to 4d. per square yard per annum according 

 to traffic. Regarding this class of pavement the Board of Commissioners 

 appointed to investigate the question of pavements for Washington, 

 United States of America, reported that " while some of the latter 

 and better class of coal tar pavements show good service, and give a 

 fair promise of reasonable durabihty, yet the general condition of 

 this class of pavements in the city is such as to lead to their condem- 

 nation as faulty in principle and deficient in vitality." 



Referring now to those inventions or methods which aim at treat- 

 ing the existing macadarri so as' to confer on it the desirable qualities 

 of dust-prevention, coolness, pleasant travel, and absence of glare, 

 they are naturally divided into two distinct classes. One class of 

 itself is dry and inert, and requires a very humid atmosphere or frequent 

 sprinkling from a watervan. Some of these processes are relatively 

 cheap to apply, but are costly if watered. Perhaps the best of this 

 class is calcium chloride, which; without the presence of water or mois- 

 ture, itself becomes a powder and rises in dust under traffic, and in 

 winter it tends to produce mud. The chief use of such substances 

 is to reduce the cost in connection with streets which are regularly 

 watered. Where water is free for city purposes, as in Adelaide, their 

 employment would be rarely justifiable on that score alone ; but the 

 less water the less wear and rutting of surface. Where they do not 

 increase the cost of watering their use may be justified. Where streets 

 are swept with horse broom every day they would have to be applied 

 daily and would generally prove too costly. 



Soluble silicate of soda and numerous other substances, which 

 become dry and powdery when absorbed into road surface, are equally 

 unsatisfactory. 



