composition whereby the lighter portions formed are carried away with the volatile hydrocarbons flowing in, the latter by constantly stirring up the fluid preventing also the very heavy portion from burning to the sides of the still.

In 1889, Mr. Dolinin constructed a continuous still for petroleum and solar oils, but as it has not been introduced in practice, a description of it is unnecessary.

Lissento's method is based upon splitting the naphtha residues between 8120 and 934° F. with a yield of 64 per cent. kerosene of 0.805 specific gravity, and 30 per cent. of 0.860 specific grauity. According to Glasenapp this method, however, is not practicable, because, 1, distillation is too slow on account of the splitting of the hydrocarbons, so that twenty times less oil can be worked than with the ordinary process; 2, the kerosene obtained is of a dark color; 3, 20 per cent. of acid are required instead of 0.5 to 2 per cent. for ordinary petroleum, and 4, crude naphtha is too cheap.

Utilization of Residuum.

The residuum obtained in the distillation of petroleum forms the crude material for the production of valuable oils, fats, etc. It represents, as a rule, a thickly fluid mass of a dark green to black-brown color, and frequently congeals at the ordinary temperature. It has an empyreumatic odor, frequently reminding one of creosote. Its specific gravity, as a rule, varies between 0.880 and 1.0, but sometimes exceeds the latter. It generally floats upon water, and is distinguished by particular fatness, especially if derived from Russian oils. After the thinly-fluid oils have been separated, it shows a high burning point, and its boiling point is generally above 572° F.

Thickly-fluid residuum, which congeals readily, generally contains paraffine, though the congelation may also be due to tarry admixtures; residuum remaining fluid at the normal temperature contains very little paraffine. After distillation the residuum is too hot to be immediately discharged without previous cooling. Besides injury to every connection of the

conduits in transferring the residuum by means of pipes, there is also to a certain extent danger of spontaneous ignition. This phenomenon of spontaneous ignition has not yet been sufficiently explained, and fortunately has been confirmed by a few cases only. It is very likely that at such a high temperature the oil vapors form with the oxygen of the air a mixture which readily ignites and explodes.

The residuum is generally cooled by means of water, a small reservoir provided with a contrivance for a constant supply of water being, as a rule, placed in the vicinity of the discharge pipe of the still. In this reservoir lies a large coil through which the residuum runs off, whereby it is sufficiently cooled to be subjected to further treatment without danger. This cooling arrangement may also be recommended for other reasons; with periodically working stills the residuum can be rapidly discharged and no time is wasted in cooling the residuum in the still itself, as is the case where no provision for cooling has been made.

In a crude state residuum is used for firing, and in a filtered and refined state as a lubricator and for the production of wagon grease and oil gas. Its use for fuel will be discussed in another chapter, while its employment for the manufacture of wagon grease and oil-gas does not strictly come within the scope of this work.

Oil residuum is also largely employed in the manufacture of asphaltic cement for street paving, which in the District of Columbia is carried out according to a method strictly prescribed. This method, in brief, is to melt the asphalt at a temperature not exceeding 325° F., and then to add the oil residuum previously heated to at least 150° F., and by continued agitation to bring the mixture to the condition of "a homogeneous cement." The specifications of the Department of Public Works of Philadelphia state that "the refined asphalt and oil residuum will be mixed in the following proportions by weight: asphalt, 100; petroleum, 16 to 22."

'Asphalt Paving. Reports of Experts appointed by Special Sub-Committees of

Not every residuum is suitable for the manufacture of lubricating oils, sufficient fluidity, which is a special advantage of Russian oils, being the first requirement, and next viscosity and purity. Russian residuum with an average specific gravity of between 0.910 and 0.920 forms an excellent lubricating material when free from water and freed by filtration from suspended tarry and coke-like constituents. Every residuum, if otherwise suitable, must as a rule be subjected to treatment with chemicals. The process is comparatively simple, and the results attained are frequently surprising. The residuum suitable for the manufacture of lubricating oil is generally treated as follows: It is brought into small agitators lined with lead and completely freed from water by means of indirect steam. It is then treated with vigorous agitation at a temperature of from 176° to 2120 F. with sulphuric acid. When the acid has for a sufficient time acted upon the residuum, agitation is discontinued, and the product allowed to stand for a short time, when the sludge acid is drawn off as rapidly as possible, the latter becoming solid at the ordinary temperature. The oil is allowed to stand for some time longer to allow particles of tar held in suspension to deposit, when it is drawn off, immediately treated with lye and boiled bright in broad shallow pans. By this treatment a green fluid of slight odor, transparent in thin layers, and of great lubricating power, is obtained from the disagreeably smelling black-brown residuum. The expense of producing such oil is however considerable, since by the treatment with acid (generally from 5 to 10 per cent.) a large portion of the residuum, frequently one-half, resinifies with the acid. According to the consistency of the residuum, thinly or thickly fluid oil is obtained, the latter being generally used as cylinder oil, while the former is brought into commerce as "vulcan oil." According to the derivation of the residuum, oils of quite a good quality may also be obtained by simple filtration; thus the American

the Citizens' Municipal Association of Philadelphia and of the Trades League (of Philadelphia to investigate Asphaltic Materials available for Street Pavements in Philadelphia. 1894.

and Galician vulcan oils (filtered vulcan oils) are filtered warm with self-pressure through filters heated by steam. A vulcan oil is supposed to be pure if a sample leaves very little or no residue upon a paper filter.

The use of residuum as such, filtered or refined, for lubricating purposes is limited, it being employed only for subordinate parts of machines, for wagon axles, etc., where special stress is laid upon a high burning point, viscosity and low price. Its use for machinery, especially steam engines and tools, cannot be recommended on account of its large content of tar, which readily causes gumming. Oils obtained from the residuum by distillation with superheated steam are almost everywhere used as a substitute for the expensive vegetable oils.

The employment of lubricating oils of mineral origin is of recent date, it having attained its present importance only within the last two or three decades. Prior to the use of superheated steam, mineral lubricating oils were prepared from the residuum by simple distillation, i. e., by vaporizing the product and condensing the vapors. Distillation was at first effected in cast-iron retorts and later on in sheet-iron stills. Although with careful distillation a product of a beautiful color and sufficiently high specific gravity was obtained, it did not possess the principal requisites of a good lubricating oil, it losing much of its lubricating power by the manner of distillation. Very high temperatures were required for vaporization, and the oil-vapors coming in contact with the over-heated sides of the still suffered partial decomposition, with the formation of lighter hydrocarbons, which decreased the fatness of the oil and imparted to it a disagreeable odor. To avoid these evils it was endeavored to destroy, or at least decrease the odor by the use of more chemicals, and to convert the oil into a tolerably useful commercial article by the addition of vegetable and animal oils. These endeavors led of necessity to improvements, and superheated steam to assist distillation was first introduced, as far as known, in Austria-Hungary by Mr. von Matscheko towards the end of the sixties or in the beginning of the seventies. The introduc

tion of superheated steam and other improvements to be mentioned later on gave rise to an industry which has at present assumed great proportions. This applies especially to the Baku district, the residuum of the kerosene distillation offering a material that is especially suitable for the production of lubricating oils. The development of this branch of industry is largely due to the labors of V. J. Ragosin, the brothers Nobel, Messrs. Schibajeff, Oehbrich, Tagieff and Sarkisow.

The oils obtained from Russian residuum are distinguished by great viscosity, capacity of resisting cold and fire, and by a minimum content of paraffine. Like the manufacture of petroleum, the fabrication of lubricating oil consists in distillation and subsequent refining of the distillate, the difference, however, being that distillation cannot be effected with the use of fire alone, but superheated steam has to be employed because the vapors formed are so heavy that they can rise only with difficulty from the still. The superheated steam acts mechanically, the object of using it being not so much to effect vaporization, which it is not capable of accomplishing on account of its comparatively low temperature, as to carry along particles of oil and by enveloping them to protect them from suffering decomposition on the hot walls of the still. The oil thus retains its lubricating power, and there is no inducement for the formation of pyrogenous products with a bad odor. The steam may be used either directly from the boiler as saturated steam with a pressure and temperature corresponding with those of the boiler, or as superheated steam.

For the distillation of crude oil saturated steam may be used under limited conditions, but only for the vaporization of the light hydrocarbons and for assisting kerosene distillation in general. For complete distillation and the distillation of residuum it is, however, entirely useless, because to attain these comparatively high temperatures it would have to be produced under a pressure which iron could not well resist, and besides, the consumption of fuel would be enormous. Hence, in the practice, superheated steam only is used for this