treatment.

dustrial requirements, are usually purified by treatment Chemical successively with sulphuric acid and a solution of caustic soda, followed by washing with water; but when the crude oil contains sulphur a special process is also adopted to remove this impurity. The lubricating-oil distillates yielded by petroleum containing Paraffin solid hydrocarbons are subjected to a low temperature, separation. when the paraffin crystallises and is separated from the oil by means of filter-presses and hydraulic presses. The paraffin is refined by treatment with animal charcoal, and may be thus rendered colourless, odourless, and tasteless.

outlined.

It will readily be understood that this is but a mere outline of the process of refining, but it will suffice to Process give a clear indication of the principle upon which the merely refiner converts the raw material into the products met with in commerce. Information respecting the character of these products will be found in the following chapter.

shale-oil

industry.

The manufacture of shale-oil carried out in Scotland Scottish commences with the destructive distillation of the shale, crude oil and ammonia being obtained in this operation. The crude oil, amounting to about thirty gallons from the ton of shale, is fractionally distilled in substantially the same manner as the petroleum, continuous distillation being adopted; but, in consequence of the comparatively complex composition of the shaleoil, the operations, though similar in principle to those of the petroleum refiner, are less simple, at least two distillations being requisite to effect the desired separation of the products.

MARINE TRANSPORT.

The building of tank steamships for the marine Tank transport of petroleum has steadily progressed, and steamers.

every recent year has seen important additions to the fleet of these vessels, some of those recently launched having a carrying capacity of as much as 8500 tons. Principles of The essential features of construction of tank steamers

(1) Provision for the expansion of the oil under an increase in temperature.

(2) Provision for keeping each tank full by automatically supplying any loss due to leakage or to contraction consequent upon a fall in the temperature of the

oil.

(3) Provision for the escape of the gases given off by

the oil.

(4) Special precautions to prevent the passage of any oil into the boiler space.

The engines and boilers are placed either amidships or at the after end of the vessel, being in either case Isolating separated from the oil-space by coffer-dams. In the coffer-dams. former method of construction the oil-tanks are both forward and aft of the machinery space, and the screwshaft is carried through the after tanks in a tunnel. Division of The oil-tanks are subdivided by transverse bulkheads, and by an amidships fore and aft bulkhead, the sides of the tanks being formed by the skin of the ship.

oil-tanks.

Ports of

the United

STORAGE AND DISTRIBUTION.

The kerosene imported into Great Britain and discharge in Ireland from the United States and Russia in bulk is Kingdom. landed at the ports of London, Liverpool, Manchester, Barrow, Bristol, Cardiff, Shields, Sunderland, Hull, Plymouth, Dublin, and Belfast. In London the principal wharves are at Purfleet, Thames Haven, Millwall, and Beckton on the Thames, and at Bromley and Bethnal Green on the Lea Cut and Regent's Canal respectively. The tank steamers discharge direct into

London Wharves.

"installa

arrange

ments.

the storage-tanks at Thames Haven, Purfleet and Beckton, and tank barges are employed for the landing of the oil at the other wharves named, the steamers lying, during the discharge, at moorings in the Thames at Greenwich and Blackwall. There are also smaller Smaller storage installations at Hammersmith, Battersea, storage Fulham, Camberwell, Hampstead, Camden Town, Bow, tions. Deptford and Greenwich, and there are many still smaller tank depôts at railway stations and elsewhere to facilitate the distribution of the oil carried by barges and tank railway-waggons. The larger storage instal- Storage lations are provided with vertical cylindrical iron or steel tanks, placed on the ground, but surrounded with a moat formed by embankments or walls, of a capacity equal to that of the tanks enclosed. These tanks are usually from about 40 to 70 ft. in diameter, by about 25 to 30 ft. in height, but in some instances are as much as 90 ft. across. The largest hold over one million imperial gallons, each inch of depth being equivalent to about 3300 gallons. Some of the tanks have a flat top with a raised edge forming a receptacle for water, and others a slightly domed top. At the distributing stations on the railways, horizontal cylindrical tanks are employed.

and

At Liverpool, the Mersey Docks and Harbour Board Installations have erected, in the neighbourhood of the Herculaneum at Liverpool Dock, a number of vertical cylindrical tanks, of about Manchester. 2000 to 3000 tons capacity each, into which the tank steamers discharge direct through an 8-inch pipe-line. There are similar installations on the Ship Canal, Manchester, and at the other ports already named.

Comparatively little kerosene is now landed in barrels. Lubricating oils are imported in bulk from Russia, but from the United States have until quite recently been wholly brought in barrels.

Under the regulations made by the Thames Conser

Petroleum spirit landed at Thames Haven, for London.

Gas-oil.

Bulk distribution of kerosene.

vancy, petroleum spirit, which is brought into the port of London in barrels from the United States, is landed at Thames Haven. Provision for the storage of petroleum spirit in barrels is also made at the ports of Liverpool and Bristol.

Gas-oil, which is imported in bulk, is to a large extent delivered direct from the steamer to the works of the gas companies, where it is stored in tanks of the usual construction.

Kerosene is largely conveyed in bulk from the main storage-installations by rail in tank-waggons, or in some instances by tank-barges on the canals, to subsidiary storage-depôts, and is thence distributed to the retailers in the road tank-waggons with which readers of this book are familiar. In this manner most of the burning oil from the refineries of the United States and Russia now reaches the retail dealer without the employment of the barrel, in which delivery was formerly made.

CHAPTER IV.

COMMERCIAL PRODUCTS OF PETROLEUM, SHALE-OIL

AND COAL-TAR.

petroleum.

CRUDE petroleum, as it comes from the well, is an oily Nature of liquid varying in physical and chemical characters crude in different districts and countries, and at different depths in the same district. It is usually of a brown colour by transmitted light, but by reflected light colour. commonly exhibits a green colour. Some descriptions are, however, so dark in colour as to appear black unless viewed in a thin stratum, and, on the other hand, crude oil is occasionally met with of a pale yellow colour. The odour of crude oil of good quality Odour. is generally considered not unpleasant, but when sulphur compounds are present in the oil the odour may be most offensive. Crude petroleum is nearly always lighter than water, its specific gravity, accord- Specific ing to the authors' experience, lying between the gravity. extremes of 771 and 1.020 (water = 1.000), but being usually a little below 800 to less than 900. The lighter descriptions are highly inflammable, and very Inflammafreely give off vapour, not only at ordinary temperatures, but even when cooled to zero Fahrenheit.

bility.

composi

tion.

Crude petroleum may be described as a complex Chemical mixture of hydrocarbons (compounds of carbon and hydrogen), ranging from the gaseous (for some descriptions of American petroleum evolve gas which has been held in solution) to the solid (paraffin wax), and we have seen in the previous chapter that the first object