BITUMEN 355 



to powder, and passed through a sieve having meshes of about one-fourth of an inch 

 square. 



The bitumen destined to render the asphalt fusible and plastic was melted, in small 

 quantities at a time, in an iron cauldron, and then the asphalt in powder was gradually 

 stirred in to the amount of 1 2 or 1 3 times the weight of bitumen. When the mixture 

 became fluid, nearly a bucketful of very small, clean gravel, previously heated apart, 

 was stirred into it ; and, as soon as the whole began to simmer with a treacly con- 

 sistence, it was fit for use. It was transported in buckets, and poured into the moulds. 

 For the reasons above assigned, I consider this addition of rounded, polished, sili- 

 ceous stones to be very injudicious. If anything of the kind be wanted to give soli- 

 dity to the pavement, it should be a granitic or hard calcareous sand, whose angular 

 form will secure the cohesion of the mass. I conceive also, that liquid bitumen in 

 moderate quantity should be used to give toughness to the asphaltic combination, and 

 prevent its being pulverised and abraded by friction. 



In the able report of the Bastenne and Gaujac Bitumen Company, drawn up by 

 Messrs. Goldsmid and Kussel, these gentlemen have made an interesting comparison 

 between the properties of mineral tar and vegetable tar : the bitumen composed of the 

 latter substance, including various modifications extracted from coal and gas, has, so 

 far as they were able to ascertain, entirely failed. This bitumen, owing to the quali- 

 ties and effects of vegetable tar, becomes soft at 115 of Fahrenheit's scale, and is 

 brittle at the freezing point ; while the bitumen into which mineral tar enters will sus- 

 tain 170 of heat without injury. In the course of the winter, 1837-38, when the cold 

 was at 14 below zero C., the bitumen of Bastenne and Gaujac, with which one side 

 of the Pont Neuf at Paris is paved, was not at all impaired, and would, apparently, 

 have resisted any degree of cold ; while that in some part of the Boulevard, which was 

 composed of vegetable tar, cracked and opened in white fissures. The French Go- 

 vernment, instructed by these experiments, has required, when any of the vegetable 

 bitumens are laid, that the pavement should be an inch and a quarter thick ; whereas, 

 where the bitumen composed of mineral tar is used, a thickness of three-quarters of 

 an inch is deemed sufficient. The pavement of the bonding warehouses at Bordeaux 

 has been laid upwards of 15 years by the Basteuno Company, and is now in a condition 

 as perfect as when first formed. The reservoirs constructed to contain the waters of 

 the Seine, at Batignolles, near Paris, have been mounted six years, and notwithstanding 

 the intense cold of the winter of 1837, which froze the whole of their contents into one 

 solid mass, and the perpetual water-pressure to which they are exposed, they have not 

 betrayed the slightest imperfection in any point. The repairs done to the ancient for- 

 tifications at Bayonne have answered so well, that the Government many years ago 

 entered into a very large contract with the company for additional works, while the 

 whole of the arches of St. Germain and St. Cloud railways, and the pavements and 

 floorings necessary for these works, have been laid with Bastenne bitumen. 



The mineral tar in the mines of Bastenne and Gaujac is easily separated from the 

 earthy matter with which it is naturally mixed, by the process of boiling, and is then 

 transported in barrels to Paris or London, being laid down in the latter place to the 

 company at 17^. per ton, in virtue of a monopoly of the article purchased by the Com- 

 pany at a sum, it is said, of 8,000?. 



Mr. Harvey, the superintendent of the Bastenne Company, was good enough to 

 supply me with various samples of mineral tar, bitumen, and asphaltic rock for 

 analysis. The tar of Bastenne is an exceedingly viscid mass, without any earthy im- 

 purity. It has the consistence of baker's dough at 60 of Fahrenheit ; at 80 it yields 

 to the slightest pressure of the finger; at 150 it resembles a soft extract; and at 

 212 it has the fluidity of molasses. It is admirably adapted to give plasticity to the 

 calcareous asphalts. 



A specimen of Egyptian asphalt which he brought me gave, by analysis, the very 

 same composition as the Val de Travers, namely 80 per cent, of pure carbonate of 

 lime, and 20 of bitumen. A specimen of mastic prepared in France was found to 

 consist, in 100 parts, of 29 of bitumen, 52 of carbonate of lime, and 19 of siliceous 

 sand. A portion of stone called the natural Bastenne rock afforded me 80 parts of 

 gritty siliceous matter and 20 of thick tar. The Trinidad bitumen contains a consi- 

 derable portion of foreign earthy matter : one specimen yielded me 25 per cent, of 

 siliceous sand ; a second, 28 ; a third, 20 ; and a fourth, 30 ; the remainder was pure 

 pitch. One specimen of Egyptian bitumen, specific gravity 1 - 2, was found to be perfectly 

 pure, for it dissolved in oil of turpentine without leaving any appreciable residuum. 



As the specific gravity of properly made mastic is nearly double that of water, a 

 cubic foot of it will weigh from 125 to 130 Ibs. ; and a square foot, three quarters of 

 an inch thick, will weigh very nearly 8 pounds. 



It has been thought advisable to preserve these remarks on bitumen, although 

 written several years ago, especially as the. recent attempts to introduce bituminous 



