Its action upon the

paraffine oil on account of the solidification of the paraffine upon the internal surface of the tank; no more heat should be employed than is actually necessary to maintain the contents in a fluid state, and the paraffine entirely melted. The same general principles of chemical treatment followed in the case of illuminating oil are observed here. The amount of acid used is much larger, and is regulated by the gravity and color of the distillate. Three, four, or even five per cent. in volume is employed. oil is very energetic, accompanied with the disengagement of an abundance of sulphurous acid vapor, and the subsidence of a heavy "acid sludge," requiring exit-pipes and stop-cocks for drawing it off, to be of larger diameter than those ordinarily employed. The "sludge" upon standing becomes quite solid, and is entirely a waste product. This treatment is followed by the usual water- and alkali-washing. Care should be taken throughout, that the proper temperature be preserved, so that the paraffine shall be maintained in perfect solution. When this operation is completed, the oil is either allowed to flow by gravity, or it is pumped into tanks, provided with a steam coil, in order that its contents may be preserved in a perfectly limpid condition to permit of the settling of the water. This being withdrawn through a stop-cock at the bottom of the tank, the contents are removed to another apartment, the temperature of which has been artificially lowered by a freezing machine, where it is subjected to the chilling process.

In the winter the ordinary temperature is sufficient to crystallize the paraffine. If the process is to be carried on

during the warm weather, the contents of the tank are barrelled, and the temperature of such a room may be reduced by a good apparatus to 10° or 15° F., even in very hot weather. An exposure of the paraffine oil for fortyeight hours to this temperature chills the whole mass to a complete solid. From the packages, the contents are shovelled out into small cotton bags of very strong material and subjected to powerful pressure by means of a hydraulic press. This pressure is slowly applied and gradually increased, the operation being one requiring skill and experience. If the pressure be too rapid and too severe, especially at the commencement, a notable percentage of paraffine crystals will be forced through the interstices of the bagging, attended also, probably, with a rupture of the same, and a serious contamination of the oil that has already passed through. Unless this operation be skilfully conducted, enough crystallized paraffine, it may be in very fine particles, will pass through the bagging, to interfere materially with the "cold-test" of the oil. In the event of a difficulty of this kind, simple straining through coarse muslin will frequently remove these coarse particles of floating crystals. This operation must of course be done in an apartment where the temperature is sufficiently cold to prevent their melting.

We have now divided the product of the distillation of the residuum into three parts: 1st. The lighter oils, which have been returned to the crude oil tank. 2d. The crude paraffine, which for the present we leave in the presses; and 3d. The refined heavy oil, which in its present shape may be either sold for lubricating purposes, or subjected to

further treatment for special purposes. The gravity of this should be about 32° B., and the fire-test 325°, and the cold-test 30° F.

Quite a high temperature is necessary to drive all the volatile portions of the residuum, and before the residue of this is completely converted into coke, the bottom of the still becomes red-hot, and yellow vapors issue from the tail pipe; very near the close of the operation the redistils over a dense, resinous, product of a light-yellow color, of a solid consistence in even moderate weather, and becoming quite brittle in cold weather. It readily sinks in water, having a specific gravity of about 1.25. It exhibits in a very high degree the iridescent properties of petroleum, to such extent indeed, that it has been supposed by some to be the peculiar compound which imparts to petroleum its rainbow hues. Professor Morton, of the Stevens Institute of Technology, who investigated its properties some years ago, obtained from it two bodies, exhibiting a high degree of fluorescence, for which he proposed the names, thallene and petrolucene. As it readily dissolves in paraffine oil, it has been added to these for the purpose of increasing their density for lubricating purposes.

For the present, we leave the further consideration of lubricating oils, and having obtained paraffine in a crude state, will take up the process of

REFINING PARAFFINE WAX.

From the refined paraffine oil, prepared and chilled as above described, there should be obtained about three

quarters of a pound of crude paraffine to each gallon of oil. The color and appearance of this will of course depend greatly upon the character of the oil from which it has been separated. When removed from the bags in which it has been pressed, it is somewhat variegated in color, some portions being of a light lemon, others presenting quite a greenish hue; the crystalline appearance thoroughly broken down by the immense pressure to which it has been subjected. The contents of the bag are thrown into a steam tank, where it is melted by live steam, one per cent. of soda-ley is added, and the whole thoroughly steamed, the condensed water withdrawn, and, when sufficiently cool to admit of the process, about 25 per cent. of benzene is added, and the whole vigorously stirred until a homogeneous mixture is obtained. The contents of this tank are ladled out into shallow tin pans holding about five or ten gallons each, which are allowed to remain in the coldair room for three or four days. This product is again expressed in clean bags. The paraffine thus obtained is in large crystals with a slight tinge remaining, and having a much higher melting point (about 130° F.) than the crude article first described. The expressed "mother liquor," from this second operation, is either run into the "stop tank" (which is a convenient receptacle for a variety of wastings, small residues of sundry distillations, etc.), or thrown back into the benzene tank for use a second time. The contents of the "stop tank," when sufficient stock has accumulated, is pumped into a still, which is generally kept for the special purpose, and the distillates proceeding

If

from this are distributed according to their character. the density should admit of it, a large percentage may be thrown direct into the tank containing illuminating oil.

Another process for the purification of crude paraffine has been employed, which is perhaps more expeditious and also more economical, but is not quite so satisfactory in its results. This consists in grinding together benzene and paraffine into a magma, which is subsequently submitted to the usual pressure. This process, which is analogous to that employed in chemical laboratories, and known as "washing crystals," is repeated until the pressed mass is white enough for ordinary purposes. For the further purification of the paraffine obtained either by this or the former process, the wax is placed in a suitable tank and gently heated, with the addition of from three to five per cent. of animal charcoal. The whole is thoroughly agitated by an air-blower for several hours. The coarser particles of charcoal are allowed to subside, and the melted wax filtered hot through a wire-gauze filter, which is lined with flannel, the filtrate passing as colorless as distilled water.

Other refiners rely largely upon the purifying action of oil of vitriol for obtaining a white product. For this purpose a wax partially purified by re-crystallization from benzene and pressure, is selected. The same is gently heated to its melting point, when about five per cent. of sulphuric acid is gradually added while brisk agitation is sustained. The action of the acid upon the melted wax is even more violent than upon the paraffine oil, and some arrangement is necessary to carry off the abundant