164 Mr. Bevan on the relative Hardness of Road Materials. 



oxalic acid and three equivalents of water. If then exposed 

 to a damp air, they increase slightly in weight by absorbing 

 water hygrometrically, and its extent varies with the humidity 

 of the atmosphere. In dry air at 70 Fahr. the crystals lose 

 some of their water of crystallization, and effloresce on the sur- 

 face. The efflorescing temperature is thus very little above 

 the ordinary heat of summer. 



XXVIII. On the relative Hardness of Road Materials. By 

 B. BEVAN, Esq. 



To the Editors of the Philosophical Magazine and Annals. 



Gentlemen, 



T AM not aware of any published experiments on the rela- 

 L tive hardness of road materials; and having for my own 

 use examined a considerable variety of substances, as to their 

 power of withstanding the percussion of a given weight, falling 

 a few inches, I take the liberty of sending the results for your 

 Magazine, if you think them sufficiently interesting. They 

 were chiefly made in 1825, and the weight used was of cast- 

 iron, falling upon the several specimens broken to the ordinary 

 size adopted in modern roads, resting upon stone, or upon iron. 

 If the weather to which these materials were exposed had no 

 effect towards their destruction, the table hereby given would 

 nearly express their relative value for the purpose of support- 

 ing the wear of a road. Such of the articles, therefore, which 

 resist the action of frost and atmospheric moisture, and have 

 the highest numbers, will be found the most valuable. 



Remaining, yours truly, B. BEVAN. 



Mount Sorrel sienite 100 



White marble 37, 31 



Chert pebbles, much used in Middlesex* 34, 27, 52, 56, 55, 65 



Quartz pebble in Bedfordshire gravel 70 



Ferruginous sandstone of Bedfordshire 20, 42 



Hurlock, from lower chalk 10 



Chalk 3 



Granite, Scotch 110 



Flint, yellow 33, 26 



Greenstone or basalt, Quittlehill, near Coventry... 110 



Sandstone, soft 13, 6 



Tile fragment 20 



Gritstone, near Brix worth, Northamptonshire ... 48,60 



Limestone, near Brad well, Bucks 5 



* These pebbles, we believe, are merely rolled chalk-flints, altered in 

 colour by the protoxide of iron contained in them having been converted 

 into peroxide. EDIT. 



Dry 



