5. After the latter is separated, the liquid portion is filtered through filters heated by steam. 6. The residue is subjected to hydraulic pressure, the expressed oil filtered, and the solid portion again used in the next operation, a sufficient quantity of fresh animal charcoal being added to make up for any loss or waste. Second Process. The raw materials, petroleum-residuum or natural ozocerite, are rendered fluid, and the liquid, after the separation of all extraneous matters, is passed through a series of charcoal filters such as are used in sugar refineries. After passing through twelve to fifteen of these cylindrical filters, the original brownish-black color of the liquid has become wine-yellow. To render it colorless and limpid as water, double the number of filters are required. The liquid acquires a lower specific gravity the less colored it becomes, but when it has become colorless, the specific gravity remains stationary no matter how long the filtration may be continued. After it has thus been freed from all bituminous matter, it is transferred to the "duplicator," where it is brought in direct contact with superheated steam and the temperature is allowed to rise to 250° C. (482° F.). Samples taken occasionally from the boiler should show no changes in the product after this temperature has been kept up for a few hours. The finished vaseline, amounting to about 25 or 30 per cent. of the raw material, is finally filtered and filled into cans for shipment. A great drawback in this method is the rapid exhaustion of the animal charcoal, which is only able to decolozire a small percentage of its own weight of crude vaseline. It is, therefore, necessary to provide extensive facilities for extracting the portion of vaseline retained by the charcoal and to regenerate the latter, which may be done by superheated steam at a temperature of 400° to 500° C. (752° to 932° F.). It is for this reason that most factories use sulphuric acid for purifying, by means of which the material may be brought to the color of beer, so that only about one-third as much charcoal is required for final decoloration. It is, however, almost impossible to get rid of the last traces of the chemicals employed, and for this reason the quality of the vaseline obtained by the other process is much superior. It is pure white, like the best tallow, and entirely tasteless. It is also odorless, not only when rubbed upon the hand, but also when melted in water; the latter property distinguishing it from all other varieties, which, on melting in water, develop a faint odor of petroleum. When melted, it yields a clear colorless liquid, which, on cooling, returns to its former homogeneous condition. Cold 98 per cent. alcohol dissolves, on shaking, 2.2 per cent. of vaseline. The residue left on evaporating the alcohol is liquid at ordinary temperatures. Hot alcohol dissolves it completely to a clear solution. On cooling the vaseline separates in flakes. It behaves in the same manner towards benzol and ether, but is not completely soluble in the latter even on warming. It does not impart an acid reaction to water, and is not affected by solution of potassa. Boiling sulphuric acid, of 1.600 specific gravity, and boiling nitric acid, of 1.185 specific gravity, have no effect on it. Fuming nitric acid colors it yellowish-red, and sulphuric acid of 1.820, grayish-black. The acid itself acquires a yellowish-brown color. The specific gravity of the vaseline is 0.848. 5 grams (2.82 drams), heated in a closed tube for several hours with oxygen, absorb from 4 to 5 cubic centimetres. Its odor is thereby rendered only very faintly acid, and its ethereal solution has only a very slight acid reaction on blue litmus-paper. BENZENE IN PHARMACY. The next most important contribution to pharmacy is the employment of benzene in extracting from plants and vegetable substances, such as seeds, etc., the essential and fixed oils, and many of the active principles. It is claimed that the essential oils so prepared have a flavor superior to those prepared by the ordinary process of distillation. M. L. Wolf, of Philadelphia, who has made some valuable contributions to our knowledge on this subject, described a process in the 'American Journal of Pharmacy' for the manufacture of apiol, and claimed his product to be a preparation equal in every respect to the high-priced French article. CHAPTER XII. PETROLEUM AS AN ILLUMINATOR. THE observation that the man who makes two blades of grass grow where only one grew before, is a benefactor to his race, finds an analogy in the assertion that he who practically adds to the span of man's life by increasing the number of hours wherein he can labor or enjoy himself, is also a benefactor. The nineteenth century has been marked in its course by a greater number of inventions and improvements, promotive of human civilization and happiness, than any like period preceding it, and, perhaps, no feature of its record is more significant or beneficent than the improved methods of lighting our dwellings, brought into use largely through the instrumentality of the great light-bearer, petroleum. Its welcome, cheerful, steady flame gladdens the cabin of the Western emigrant on his trail through the trackless forest, and lights up the hut of the Colorado miner. It cheers equally the home of the thrifty farmer, and the rude quarters of the humblest laborer. Its bright rays lend their kindly aid to the thousand homely cares, which give zest and happiness to the family circle. Thus the sum of human knowledge is increased and the aggregate of wealth added to by the useful occupancy of hours snatched from darkness and sleep, and thus practically man's life has been extended, and his opportunities for usefulness increased. The circumstances, which have led up to the present general use of the hydro-carbon light, are varied. The torch or flambeau of the Russian peasant of the Caucasus, or the rude smoky lamp of the Rangoon laborer, afforded a small margin to the inventor to hope for improvement. The excess of carbon in the "earth oil" used by these, would not permit the same appliances in use for the refined and pure vegetable oils then employed; nevertheless, the great abundance in certain localities of this "earth oil" overcame by degrees the repugnance to its use, occasioned by its disagreeable odor, both in its natural state and when it was being burned. No efforts had yet been made either to purify it, or to construct suitable lamps to use it. Its chemical composition was either wholly undetermined, or remained locked up in the memoranda of the chemist. It was not even suspected, that the large proportion of carbon it contained, required a special burner to secure thereby a large supply of oxygen, by which its best illuminating effects could be developed. M. Felix Foucon, in an article in the Revue des Deux Mondes,' very interestingly alludes to the part which the several nations have contributed in bringing so useful a discovery to perfection. "In the domain of the useful arts, each age reveals characteristic tendencies. In the last century mankind had need to clothe themselves cheaply. It was this, that made the fortune of Arkwright and the machine spinners, the |