Page:Encyclopædia Britannica, Ninth Edition, v. 18.djvu/258

240 PARAFFIN more fully than other experimenters had ever done the conditions prevailing in the working of steam-boilers ; the only difference was that he took care to collect all the heat produced in a large mass of water of known weight, and measured the heat by the increase of temperature produced in this heat receptacle. He found that even heavy Virginia lubricating oil gave not more than 10,180 units of heat (Centigrade) per unit-weight of fuel burned. But, on the other hand, in direct experiments made by Scheurer-Kestner, a coal containing 88 4 per cent, of carbon, 4 4 of hydrogen, and 7 "2 per cent, of oxygen, nitrogen, and ash gave 9628 units of heat, while another coal of the same elementary composition gave 9117 units. Gas retort coke (though a far closer approximation to pure carbon) yields only 8050 units. Supposing coal yielded just that in opposition to the 10,000 units from petroleum, it is clear that the latter must not cost more than 1 25 times as much as coal weight for weight, or else it is the more expensive fuel. Take one ton of coal at 10s.; eight- tenths of a ton of petroleum is its calorific equivalent ; but this weight of the oil (taking the specific gravity at 8) measures 224 gallons. Hence petroleum, to be as cheap as coal, must not cost more than about a halfpenny a gallon. Cheap as mineral oil is nowadays, it has not yet come down to this level. To pass to the lubricating oil (third class), it, like the burning oil, competes with the fats and fatty oils which until lately were exclusively employed. In opposition to these it offers other and very substantial advantages besides its lower price. Good mineral lubricating oil may have such very high flashing point that it may be positively less inflammable than fatty oils or tallow ; and, as a lubricant for high pressure steam cylinders, it offers the great advantage that it is not, like fatty oils, decomposed by hot steam into glycerin and fatty acids, which latter cannot but attack the metal of the machinery to some extent. A still more important feature in mineral lubricating oil is that, even when diffused throughout a mass of cotton (or other textile) waste, it shows no tendency towards spon taneous combustion. In exhaustive experiments by Galletly and by Coleman, it was found that mineral lubricating oils diffused through textile waste do not take fire at temperatures at which even colza oil ignites, and also that fatty lubricants to which from 20 to 50 per cent. of mineral oil was added were thereby prevented from igniting. Solid paraffin, industrially and commercially, is a sub stitute for the more expensive stearin as a material for candles. To this latter it is more than equivalent in light- giving power ; but it offers the drawback of greater soft ness and lower fusing point. In practice paraffin is always alloyed with stearin to produce candles possessing the necessary degree of hardness and stability of form. The Paraffin Oil Industry of Scotland. In December 1847 Lyon Play fair drew the attention of the late Mr James Young, F.R.S., a Glasgow chemist, to a spring or exuda tion of petroleum at Alfreton in Derbyshire, and induced him to lease the spring, with the view of turning the material to commercial advantage. In 1848 -Mr Young commenced the purification and preparation from this petroleum of two varieties of oil one, thick, for lubricating, the other, thin and limpid, for burning in lamps. It was found that this crude petroleum contained paraffin in notable proportion ; but the solid paraffin was not separated for trade purposes, and that body continued still a simple chemical curiosity. Within two years the quantity of petroleum yielded by the spring began to decrease, and in the beginning of 1851 it was practically exhausted, and the business there ceased. Meantime it had occurred to Mr Young that the petroleum lie was working might have been produced by the action of heat on the underlying coal ; and, under the impression that it might be possible by artificial means to pro duce a similar substance, he began an extensive series of experiments on the destructive distillation of coal. As the result of a lom -con- tinned iiivestigalion in this direction, with many varieties of coal, Mr Young in October 1850 secured a patent for the manufacture of j paraffin and paraffin oil from bituminous coal, which patent became the basis of the new industry. "The coals, " the patentee says, " which I deem to be best fitted for the purpose are such as are usually culled parrot coal, cannel coal, and gas coal, and which are much used in the manufacture of gas for the purpose of illumination." Early in 1850 Mr Young s attention was called to the Boghead mineral, which he found to be of all the substances experimented upon the most promising for his purpose. That circumstance determined Mr Young and his original partners to set up their works at Bathgate in the region of the Boghead mineral, where con sequently, in 1850, the necessary buildings and plant were erected, and manufacturing operations were begun in 1851. In 1853 a law suit of great importance, which turned on the scientific question " What is coal ? took place between the proprietor of a portion of the Boghead mineral and his mineral tenant, who was entitled to work coal only. The proprietor averred that the mineral in question was not coal ; but, after a great amount of scientific evidence on both sides had been heard, the decision was that the substance came, so far as regarded the purposes of the lease, within the definition of coal. Had the issue of the case been in favour of the proprietor of the mineral, Mr Young s patent would have been practically valueless, for he claimed only the distillation of bituminous coal. The dis tillation of mineral schists or shale at a low red heat had, moreover, been previously patented by Du Buisson ; and the only raw materials which have been used to any extent in the Scottish industry are the Boghead mineral and subsequently bituminous shale. The essential feature of Young s invention was the distillation of bituminous substances at the lowest temperature at which they could be volatilized to a practically sufficient extent. In practice it was found that a temperature of 800 F. is the point about which the best results are obtained. The material exclusively distilled in the early years of the industry in Scotland was the Boghead cannel or Torbanehill mineral. The supply of this mineral was limited, and, as its value for gas-making as well as for oil -distilling was very great, it rapidly advanced in price from 13s. 6d. per ton, at which it was contracted for when the Bathgate works began operations, till it rose to 90s. per ton before its final disappearance from the market about 1866. As early as 1859 the bituminous shales which are found in the Scottish Carboniferous formation began to attract attention as a possible source of raw material for the industry, and in that year a seam was experimentally opened up at Broxburn, Linlithgowshire. In 1861 a shale oil work was established at Gavieside, West Calder, and by the period of the expiry of Young s patent in 1864 several works distilling shale were in operation. But, while from the Bog head mineral from 120 to 130 gallons of crude oil were obtainable for every ton distilled, the ordinary bituminous shales yield at most only 35 gallons per ton ; and even with the improved methods of working in use at the present day the average yield of crude oil from shales is not more than 32 gallons per ton. The bituminous shales of Scotland are found in a wide belt of the Carboniferous formation, extending from Ayrshire in a north-easterly direction to the Fife coast. In Ayr and Renfrew they are found to some extent in the true Coal-measures; but, generally, and especially in the east, they are obtained in the Lower Carboniferous series. These oil shales consist of fissile argillaceous bands, highly impreg nated with bituminous matter. As a rule the shale of the west country yields a high percentage of crude oil, but the Linlithgow, Midlothian, and Fife shales produce oils comparatively rich in lubricating oil and solid paraffin, the most valuable product of the industry. The ordinary Broxburn shale contains 17 per cent, of bituminous volatile matter, and leaves 76 per cent, of spent shale (char) on distillation. In contrast with this is the composition of the Boghead mineral, which contained not less than 65 per cent, of volatile bituminous matter and only 22 per cent, of ash. In the early years of the industry at Bathgate, the two classes of oil heavy (lubricant) and light (illuminating) were the products to which attention was principally directed. Paraffin was separated from the heavy oils ; but the demand for it was at first small, and many difficulties had to be overcome before candles consisting principally of that body could be favourably brought into the market. With the increased knowledge, improved methods, and eager competition of the present day, the range of products has largely extended, and almost everything obtainable from the shale, except the incombustible ash, is turned to profitable account. The commercial products embrace sulphate of ammonia, illuminating and heating gas, gasoline and naphtha, highly volatile oils, several grades of burning oil and of lubricating oil, heavy green oil used for making oil gas, and solid paraffin. The sequence of manufacturing operations has not changed in any essential particular since first established by Young ; but at every stage and in all the appliances numerous and important modifications have been, and continue to be, actively introduced, all tending to greater economy of work, increase of production, and improvement of the quality and variety of commercial products.