A text-book of assaying

by C. Beringer; J. J. Beringer

The assay of these is carried out in the same way as that of coals, but the volatile matters are separately examined, and, in consequence, a larger quantity of material must be used. For the moisture, volatile matter, fixed carbon and ash, the determinations are the same, but a special distillation must be made to obtain a sufficient quantity of the volatile products for subsequent examination. Take 500 or 1000 grams of the well-sampled and powdered shale, and introduce into a cast-iron retort as shown in fig. 74. Lute the joint with fire-clay, place the cover on, and bolt it down. The bolts should have a covering of fire-clay to protect them from the action of the fire. Place the retort in a wind furnace, supporting it on a brick, and pack well around with coke. Build up the furnace around and over the retort with loose fire-bricks, and heat gradually.

As soon as water begins to drip, the tube of the retort is cooled by wrapping a wet cloth around it, and keeping wet with water. The water is kept from running into the receiver by a ring of damp fire-clay. A quantity of gas first comes over and will be lost, afterwards water and oily matters. The retort must be red hot at the close of the distillation, and when nothing more distils off, which occurs in about two or three hours, the wet cloth is removed, and the tube heated with a Bunsen burner to drive forward the matter condensed in it into the receiver, and thus to clean the tube. It can be seen when the tube is clean by looking up through it into the red-hot retort. The receiver is then removed, and the retort, taken from the furnace, is allowed to cool. When cold it is opened, and the fixed carbon and ash weighed, as a check on the smaller assay.

The distillate of water and oil is warmed, and will separate into two layers, the upper one of which is oil, and the lower water. These are measured, and if the specific gravity of the oil is taken, its weight may be calculated. If the two liquids do not separate well, the water may be filtered off, after cooling, through a damped filter. The separation is, however, best effected in a separator (fig. 75). The liquids are poured into this, allowed to settle, and the lower layer drained off. The volume of the water is measured and its weight calculated in per cents. on the amount of shale taken.

Examination of the Oil.—A sufficient quantity of the oil must be got, so that if one distillation does not yield enough, the requisite quantity must be obtained by making two or more distillations. The oils are mixed, and the mixture, after having had its volume and specific gravity ascertained, is placed in a copper retort, and re-distilled with the aid of a current of steam. The residue in the retort is coke.

The distillate is separated from the water by means of the separator, and shaken for ten minutes with one-twentieth of its bulk of sulphuric acid (sp. g. 1.70). The temperature should not be allowed to rise above 40°. Allow to stand, and run off the "acid tar."

The oil is now shaken up with from 10 c.c. to 20 c.c. of sodic hydrate solution (sp. g. 1.3), allowed to stand, warmed for half-an-hour, and the "soda-tar" run off.

On mixing this soda-tar with dilute acid, the "crude shale oil creosote" separates, and is measured off.

The purified oil is next re-distilled in fractions, which come over in the following order:—"Naphtha," "light oil," "heavy oil," and "still bottoms." For the first product, which is only got from certain shales, the receiver is changed when the distillate has a specific gravity of 0.78. For the second product the process is continued till a drop of the distillate, caught as it falls from the neck of the retort on a cold spatula, shows signs of solidifying. This is "crude light oil."