Paraffin

The oil and soft wax that sweats out during the process are divided into fractions, graded according to their setting points.

The first runnings from the trays up to a set point of about go° F, termed "light foots oil," is in the ordinary process used as works fuel ; it has no other commercial value and the wax it contains is of too low a melting point to justify repressing or further redistillation.

The next fraction sweating out, from a set point of go° to Ho° F, termed "heavy foots oil," is generally pumped back for incorporation with the wax distillate cut from the crude oil.

Wax that sweats out above this point till the end of the oper ations is reached is re-sweated to give a wax of a lower grade, or if only one grade of finished wax is being made it is mixed with the scale from the filter-presses to make up the next sweat ing chamber charge.

The setting points and fractions obtained are, of course, purely arbitrary and are governed by the number of the grades of finished wax being made, as well as by the method and tem peratures used in processing the wax. It still contains colouring matter and therefore must be decolorized.

The Finishing Treatment.

In many refineries the wax is melted and run into agitators, where it is treated with successive amounts of strong sulphuric acid. The agitators are lead-lined and steam-jacketed and the mixture of acid and wax is violently stirred up by air agitation. The agitation is carried on for 3o min., and then an hour is allowed for settling. At the end of this time the acid sludge is drawn off and the melted wax is run into another agitator, in which it is washed with hot water and then with caustic soda and finally with a hot water spray. After removing all traces of water by long settling, the wax is dried finally by blowing air through it. Alternatively the use of caustic soda may be dispensed with by following up the acid treatment with agitation in the presence of finely divided absorbent clay. Even at this stage the wax is not entirely colourless and odour less and it is necessary to filter it through ignited fuller's earth.

Another method of treatment that has been found very effective and that dispenses with the acid treatment altogether is achieved by filtering the wax-scale through recently ignited bauxite. This mineral is essentially a mixture of alumina and ferric oxide and has a very porous structure. To prepare it for use, the crude rock is ground and sieved to form coarse particles that pass through a 1 o-mesh sieve and are retained on a go-mesh sieve. The bauxite is then passed through a furnace at about 600° C, where it is ignited and becomes substantially free from water. The bauxite is now put into filters that are jacketed and the melted wax is allowed to flow through, samples being tested to see that the colour of the effluent wax is up to standard. The wax is run to trays, allowed to solidify, and packed in bags ; each cake of wax is about 1 2 in.X 18 in.X 1 4 in. in dimensions and weighs about 1 of lb.

Refined wax is always passed through a filter-press equipped with double sheets of filter paper before final caking. The wax should be entirely odourless and a cake of wax freshly broken should possess no smell at the plane of fracture. It should be colourless, stable to heat and light, and of the correct melting point. It should be free from opaque blemishes ("mottling") and should not be crumbly or flaky. It is sold commercially in terms of melting point, e.g., hard wax in the grade that melts between 13o° F and 135° F.

It has been found in the case of certain sulphurous oils that a preliminary treatment with alkaline hypochlorite before filtration materially assists in the production of a non-odorous wax.

Amorphous Wa

the pressable wax has been distilled off from the crude oil residue there appears a fraction containing wax, the crystal size of which is very much smaller than that of the preceding fraction; this is the so-called amorphous distillate.

Until recent times fractions and residues of petroleum con taining this material that could not be handled in filter-presses were allowed to stand, well diluted with petrol, in tanks at a low temperature and for a long period of time. The slow impercep tible action of gravity gradually precipitated the slightly heavier wax out of the slightly lighter solution. There was left at the bottom of the tank a soft salve-like mass and above it a petrol solution of de-waxed oil. In many cases the precipitate was so amorphous that it could be worked up for petroleum jelly and this was particularly the case when a residue was being treated.

A revolutionary idea has changed this procedure. It is to the credit of Sharples, who had successfully separated cream from milk by means of high speed centrifuges to apply this method to the separation of amorphous wax from its accompanying oil.

fibres before weaving, and very large amounts of water-proofed textiles are now manufactured. The softer paraffins are used in the manufacture of ointments and salves, and a large amount is applied in rendering match sticks water-proof and flammable.

The above uses, however, are only minor when compared with the vast quantities used in the manufacture of tapers, candles and night lights. In making candles it is not usual to employ pure paraffin, because it has a tendency to stick to the moulds and, moreover, may soften too easily in service, so the paraffin is mixed with stearic acid and foalmitic acid that are obtained by the decomposition of many natural fats. The effect of the stearic acid is to give a less plastic composition, one that is stiffer and not so likely to bend in warm weather.

The earlier candles were usually made of tallow, were very soft and the wick required constant snuffing, but in the modern wax candle the wick is so woven that it tends to bend over during burning and so be consumed in the hot edge of the flame as fast as the burning proceeds. (A. E. D.)