Discoveries and Inventions of the Nineteenth Century

Why, then, one formula rather than another? The answer to this question is the statement of a theoretical law upon which the whole science of modern chemistry is based; for it has the same relation to that science as gravitation has to astronomy. It is a matter of fact that all gases, whatever their chemical nature, expand alike with the same application of heat, and all obey the same law, which connects volumes and pressures. These are very remarkable uniformities, for gases in this respect exhibit the most decided contrast to liquids and solids. The volume of each solid and of each liquid has its own special relations to temperature and pressure: here 759there is endless diversity. The volumes of all gases have one and the same relation to temperature and pressure: here there is absolute uniformity. As an explanation of these and other facts relating to gases, Amedeo Avogadro, in 1811, put forward this hypothesis—Equal volumes of all gases, under like circumstances of temperature and pressure, contain the same number of molecules. This hypothesis was revived by Ampère a few years later, and sometimes is called his. A necessary consequence of this law is that the weights of the molecules of gases are proportional to their densities or specific gravities. Hence when the percentage composition of a hydro-carbon has been determined, by burning or oxidizing it in such a manner as to obtain and weigh the products, carbonic acid and water, the next thing the chemist does is to obtain the weight of a volume of the gas. The number of times this exceeds the weight of hydrogen gas, under the same conditions, expresses how many times the molecule is heavier than the hydrogen molecule. Now, the chemist’s unit of weight in these inquiries is the weight of a single atom of hydrogen; and, as there are grounds for believing that the molecule of hydrogen consists of two atoms of that substance, its weight = 2. Now, if the molecule of marsh gas, the first hydro-carbon in the above list, has the composition assigned, it will be 12 + 4 = 16 times heavier than the atom of hydrogen, and 162 = 8 times heavier than the molecule of hydrogen. Hence, if Avogadro’s law be correct, marsh gas should be just eight times heavier than hydrogen gas; which is really the fact. The formula expressing the composition of the molecule of a hydro-carbon, or of any chemical compound whatever, is always so fixed that the same relations may hold; and almost the first thing a chemist does in examining a new body is to endeavour to obtain it in the state of gas. The first four members of the series headed A are gases at ordinary temperatures, the fifth is a gas at temperatures above the freezing-point, and a liquid at lower temperatures; the next following members are liquids which boil (that is, are converted into gases) at temperatures rising with each additional carbon atom about 20° F. The specific gravities and boiling-points of these liquids augment as we pass from one hydro-carbon to the next, and the lower members of the series are solids, fusing at temperatures higher and higher as the number of carbon atoms is greater. Similar gradations of properties are exhibited by the other series of hydro-carbons. Petroleum or rock-oil is the name given to liquid hydro-carbons found in nature, and consisting chiefly of compounds belonging to the series marked A in the above list. Some varieties of petroleum hold in solution other hydro-carbons, and in some cases paraffin is extracted from the oils by exposing the liquid to cold, when the solid crystallizes out. Paraffin is a solid belonging to the B series, and it is for the most part obtained by heating certain minerals. Deposits of liquid hydro-carbons, perhaps formed by a kind of natural subterranean distillation from coal or other fossil organic matter, exist in various localities. These deposits have long been known and utilized at Rangoon, in Burmah, and on the shores of the Caspian Sea. At Rangoon the mineral oil is obtained by sinking wells about 60 ft. deep in a kind of clay soil, which is saturated with it. The oily clay rests upon a bed of slate also containing oil, and underneath this is coal. It may be supposed that subterranean heat, acting upon the coal, has distilled off the petroleum, which has condensed in the upper strata. This petroleum, when distilled in a current of steam, leaves about 4 per cent of residue, and the volatile portion contains about one-tenth of its weight of a substance (paraffin) 760which is solid at ordinary temperatures. After an agitation with oil of vitriol, and another distillation, rock oil or naphtha is obtained, which, however, is still a mixture of several distinct chemical compounds. Mineral oils have also been found in China, Japan, Hindostan, Persia, the West India Islands, France, Italy, Bavaria, and England. In one of the Ionian Islands there are oil-springs which have flowed, it is said, over 2,000 years. But it is the recently discovered and extremely copious springs and wells in Pennsylvania and Canada which have given a vastly extended importance to the trade in mineral oil. Rock oil is now used in enormous quantities as the cheapest illuminating oil, and that which furnishes the most intense light. Its consumption as a lubricating oil for machines has also been very large. Mineral oil was occasionally found at various places in the United States, and sometimes used by the inhabitants of the locality before the recent discoveries; but it was not until August, 1859, that it was met with in large quantities. About this time a boring which was made at Oil Creek, Pennsylvania, reached an abundant source, for 1,000 gallons a day were drawn from it for many weeks. The news of the discovery of this copious oil-spring spread rapidly: thousands of persons flocked to the neighbourhood in hopes of easily making a fortune by “striking oil.” Before the end of 1860 more than a thousand wells had been bored, and some of these had yielded largely. The regions of North America in which petroleum has been found cover a large part of the States, and comprise Pennsylvania, New York, Ohio, Michigan, Kentucky, Tennessee, Kansas, Illinois, Texas, and California. In the vicinity of Oil Creek the bore-holes are usually about 3 in. or 4 in. in diameter, and are often 500 ft. deep, and even 800 ft. is not uncommon. To make a bore-hole 900 ft. deep, and procure all the requisites—steam engines, barrels, &c., for pumping the oil—costs about $5,000. In 1869 many of these wells still yielded regularly 300 barrels a day, but the supply has not continued with the same abundance. One of the luckiest wells flowed at its first opening at the rate of about 25,000 barrels a day. The apparatus used for working the oil-wells is very simple—a rude derrick, a small steam engine, a pump, and some barrels and tubs being all that is necessary. Fig. 345 will give the reader an idea of the scene presented by a cluster of oil-wells in the Oil Creek region. Oil Creek received its name before the petroleum trade was established, from the oil found floating on the surface of the water. It is on the Alleghany River, about 150 miles above Pittsburg, and here at its mouth is situated Oil City. There is a wharf in Pittsburg for the oil traffic, and the barrels are brought down the river in flats, or the oil is poured into very large flat boxes, divided into compartments, which are then closed, and the boxes floated down in groups of twenty or more. The refining process consists in placing the crude oil into a large iron retort, connected with a condenser formed of a coil of iron pipes, surrounded by cold water. Heat is applied, and the lighter hydro-carbons (naphtha) come over first. After the naphtha, the oils which are used for illuminating purposes distil off. A current of steam is then forced into the retort, and this brings over the heavy oils which are used for greasing machinery. A black tarry oil yet remains; and, finally, after the separation of this, a quantity of coke. The products are subjected to certain processes of purification, which need not here be described. The magnitude of the American oil trade may be inferred from the fact that in the second year of its existence, from January to June, 1862, more than 4,500,000 gallons were exported from four seaports. This can hardly be wondered at, considering the extremely low 761price at which this excellent illuminating and lubricating agent can be produced. Refined petroleum can be bought at Pittsburg for 16 cents. per gallon. It is believed by some that the supplies of petroleum which exist in various localities are so abundant that they will furnish illuminating oils to the whole world for centuries. Fig. 345.—View on Hyde and Egbert’s Farm, Oil Creek. PARAFFIN. In the course of some researches on the substances contained in the tar, which is obtained by heating wood in close vessels, Reichenbach found a white translucent substance, to which he gave the above name, because it was not acted upon by any of the ordinary chemical reagents, such as sulphuric acid, nitric acid, &c. This substance, which is composed of carbon and hydrogen only, is not unlike spermaceti; it is colourless, translucent, and without smell or taste. But when slightly warmed, it becomes very plastic, and may then be moulded with the greatest ease—and in this respect it differs from spermaceti. Paraffin melts at from 88° to 150° C., to a colourless liquid, which is so fluid that it may be filtered through paper like water, and at a higher temperature it can be distilled unchanged. Paraffin does not dissolve in water, and is but slightly soluble in alcohol. In ether, naphtha, turpentine, benzol, and sulphide of carbon, it dissolves very readily. When heated with sulphur, it is decomposed: the sulphur seizes upon its hydrogen, sulphuretted hydrogen is given off, and the carbon is separated; and this action has been proposed as a ready means of obtaining pure sulphuretted hydrogen for laboratory use. It is probable 762that paraffin is a mixture of various hydro-carbons, having a composition expressible by the formula, CnH2n; for different specimens fuse at different temperatures, according as the paraffin has been obtained from one or the other source. In the year 1847, Dr. Lyon Playfair directed the attention of Mr. James Young, then of Manchester, to a dense petroleum which issued from the crevices of the coal in a Derbyshire mine. It was soon found that this substance yielded a distillation—a pale yellow oil—which, on cooling, deposited solid paraffin. Mr. Young, recognizing the importance of this discovery, had an establishment at once erected on the spot, and the work of extracting paraffin was carried on until the supply of the petroleum had become nearly exhausted. Forced to seek for other sources of paraffin, Mr. Young was fortunate enough, after many trials, to discover that a species of bituminous coal, which occurs at Boghead, near Bathgate, in the county of Linlithgow, yielded by distillation annually large quantities of paraffin. In 1850 he procured a patent for “treating bituminous coals to obtain paraffin, and oil containing paraffin, therefrom.” This method consisted in distilling the coal in an iron retort, gradually heated up to low redness, and kept at that temperature until the volatile products ceased to come off. Under this patent, Mr. Young developed the manufacture of paraffin into a new and important branch of industry. The oil which first comes over in the distillation of the Boghead mineral is largely used for illuminating purposes under a variety of names besides that of paraffin oil, which term is, we believe, chiefly applied to a less volatile portion, extensively used for lubricating machinery, and consisting of liquid hydro-carbons of the same percentage composition as solid paraffin, which substance it also holds in solution. Mr. Young’s process consisted in placing the mineral in a retort encased in brickwork—an arrangement which caused the temperature of the retort to be more