ASPHALTUM AND BITUMINOUS ROCK 405 



in places subject to foj^s, rains, and low tomporaturos, for the 

 reason that it becomes polished and sli])pery vvlien wet, or 

 dry in cold weather. In Paris and HoiTm Inr^o supplies of 

 sand are kept near the streets paved with asphahic liiiicslone 

 for use during fog, slight rain, or snow. 



Pavements made with Trinidad or other asi)]ialluin in 

 which sand, in proportions up to 80 per cent, is tlie cliief in- 

 gredient, do not become slippery except when covered witli 

 ice; the sand makes them gritty and not susceptible to i)olish. 



For the manufacture of black vaniish, used chiefly for 

 coating ironwork, pure asphaltum is dissolved in benzole or 

 liquids containing benzole. The asphidtum from Syria is 

 used for this purpose. By covering hot iron with asphaltum 

 varnish, the volatile ingredients of the latter are driven olT, 

 leaving a residual coating in the form of a smooth and polished 

 enamel. 



For insulating and cementing purposes asi)haltum forms 

 a very important ingredient on account of its wonderfully 

 adhesive quality. 



For waterproofing foundations of brick or stone, asphal- 

 tum is dissolved in petroleum and laid in the form of a cement 

 or mortar, formmg a veiy durable wateiproof coating. 



For making cement, petroleum residue is added to asphal- 

 tum m order to render it plastic, and from 5 to 10 per cent of 

 sharp sand is mixed with it, according to the pui-^^ose for which 

 it is to be used. 



For roofing purposes asphaltum is used to a ver>' large 

 extent in admixture with coal tar, pitch, or petroleum residue; 

 the material being used to saturate two or three thicknesses 

 of felt, which are finally compressed into one compact sheet. 

 The tar or roofing felt is held in place by nails driven through 

 tin disks, and the whole completely covered with cement simi- 

 lar m composition to that used in making the felt ; while this 

 is still soft, a covering of sharp sand, or screened gravel, is 

 spread over the surface, forming a tight roof of great dura- 

 bility. 



There are various methods used for the refining of as- 

 phaltum, depending on the nature of the crude material and 

 the use to which it is to be applied. In general, wit h high grade 



