This imperfect combustion produces smoke and imparts to the atmosphere of the room unpleasant odors, and not infrequently leads to an explosion of the lamp and disastrous conflagrations. The steady flow of the oil through an unencumbered wick keeps the wick burner comparatively cool, and prevents the heating of the lamp and of the oil within it; but, when the capillarity of the wick is impaired, the burner, lamp and oil within it become heated to a temperature that finally produces a distillation of the lighter portion of the oil, in many instances causing the flame to become dense and smoky; sometimes streaming above the top of the chimney; and, if not speedily extinguished, resulting in an explosion and the destruction of the lamp.
When the normal and cracked oils are mixed, the mixture partakes of the mingled characteristics of the constituents. The mixture may be nearly as good as the normal oils, or nearly as bad as the cracked oils. At the present time the common kerosene sold is either a "cracked" or a "mixed" oil, while the bulk of the high-test kerosene is supposed to consist of "normal" oil; and, while any or all of these oils may be of any required test, they are of very various quality in other respects.
The test of an oil, "high" or "low," represents the temperature to which the oil must be heated in order that a suitable quantity—usually one half-pint—may give off a sufficient amount of inflammable vapor to either flash or burn. The temperatures at which the same oil will flash and burn vary greatly with the character of the oil, being from 10° to 50° apart by Fahrenheit's scale. While it has been repeatedly demonstrated, by several of the most eminent scientific experts now living, that the temperature at which an oil will burn is of no importance as an indication of its safety, this test is still in use in many localities. It is, however, the temperature at which the vapors will flash that is usually understood as the "test" of an oil, and it varies from 70° to 90° Fahr. in low-test oils to 120° to 140° in high-test oils. Experiment has repeatedly demonstrated that an oil that will give off vapors that will flash at 100° Fahr. is safe for any legitimate use. As painful and disastrous accidents are liable to follow the explosion of a lamp, and as the increased danger of explosion where low-test oils are used is obvious to any reflecting person, all efforts to restrict the manufacture or sale of unsafe oils by legislation have been hitherto directed toward the exclusion of very low-test oils from the market. In England such legislation has been based upon very elaborate research, and has been in the main successful; but in the United States no less earnest though less carefully considered measures have been embodied in legislation which has resulted in the enactment of a great variety of statutes—giving to some States laws unreasonably exacting, to others wise provisions, while yet others have no legislative restrictions whatever. Of course, such diverse enactments relating to a
