Petroleum is an example of several fluids, heavier than water, which are liable to ignition, or explosion, or both, when their vapour comes into contact with flame or a body at a high temperature. All such fluids (for instance, carbon bisulphide) may be rendered quite innocuous by storing them under a layer of water. A convenient tank for the purpose is shown in Fig. 5: o, space for mineral oil or other fluid to be stored; 6, diaphragm; o, balance - pipe; d, filling and emptying pipe for fluid; e, inlet and overflow water-pipe; f, vent-pipe; g, water layer above the fluid; A, water layer beneath the fluid. The tank is first filled with water by the pipe d, entering immediately under the diaphragm; the admission of water is continued until it has passed up the balance-pipe c, and filled the space g, driving out the air by the vent f, the petroleum or other fluid in then forced through d, displacing the water, which passes up c, into g, the surplus escaping by the outlet e. When the rent / is closed, no air can mingle with the contents, and no evaporation can take place.
In order to draw fluid out, water is forced in by e.
With regard to the material for the construction of petroleum receptacles. Dr. Stevenson Macadam states that lead will spoil lamp oil in a week or less; iron does not detract from the illuminating qualities, but deepens the colour and causes a rusty deposit; zinc, solder, and galvanised iron are all deleterious. Metals which do not seriously dinnage the oil, but which still cause its deterioration by contact prolonged for months, are tin, copper, and tinned copper, common solder containing lend being excluded from use in their manufacture. Stoneware, slate, and enamelled iron are therefore recommended.
It has been asserted that the addition of a little powdered soapwort (Sapanaria officinalis), digested in water, to petroleum, causes it to form a solid mucilage, and that the subsequent application of a little phenol (carbolic acid) causes it to resume perfect limpidity.