144 TIIK I'AIIKS AND GARDENS OF PAIUS. [Vn.w. IX. 



Bituminous limestone occurs naturally in many parts of the 

 ^Yorld, notably at Yal de Travers, in the Canton of Neufchatel, 

 Switzerland, and at Pyrimont, near Seyssel, a small town in the 

 department of x\in, on the right bank of the Khone. The asphalte- 

 rock near Pyrimont consists of pure limestone impregnated with 

 about ten per cent, of fossil or natural bitumen. It may be asked 

 how it is that ordinary tar or pitch of good quality mixed with 

 pounded limestone does not answer the purpose of this natural 

 combination ; but it is found by experiment that, although natural 

 bitumen differs but slightly in chemical composition from pitch 

 and tar, it is much more elastic and durable. If made with tar, 

 the resulting asphalte is sticky and soft in hot weather ; if with 

 pitch, it is too brittle, and soon cracks and splits. 



In the natural asphaltic rock the bitumen is so intimately 

 combined with the calcareous matter, that it not only resists the 

 action of the air and water for a considerable time, but even that 

 of some of the strong mineral acids. The ancients were in the 

 constant habit of using natural bitumen instead of mortar. The 

 principal ingredients used in forming the mastic for the pavement 

 is the dark brown bituminous limestone from Pyrimont, just 

 described. The stone is first reduced to fine powder, and then 

 mixed with a certain proportion of mineral bitumen, extracted 

 previously from another portion of it. 



"When it is intended to be used for covering roofs, lining tanks, 

 etc., no other addition is necessary ; but if it is to be used for 

 paving, a certain quantity of sea-grit is added. One specimen 

 analysed by an English chemist yielded 29 of bitumen, 52 of 

 limestone, and 19 of siliceous sand. The ingredients are exposed 

 for some hours to a strong heat in large cauldrons, and kept 

 constantly stirred by machinery. The mastic thus formed is 

 made into blocks, measuring eighteen inches square by six inches 

 deep, and weighing from 1121b. to 1301b. each. In this state 

 they are sold ready for use and are remelted on the spot where 

 the asphalte has to be applied ; for which purpose small portable 

 furnaces fitted with cauldrons are employed. A pound weight of 

 mineral bitumen is first put into the cauldron, and when melted 

 561b. of the mastic is added, the whole being repeatedly stirred. 

 When fully mixed, another 561b. of mastic is stirred in, and so 

 on until the cauldron is full. When thoroughly melted — which 



