It has been found that variations in barometric pressure affect the flash-point and accordingly corrections have to be made in obtaining strictly comparative results at different pressures.
To illuminating oil or kerosene a series of tests is applied in order that the colour, odour, specific gravity and flash-point or fire-test may be recorded.
It is still customary to determine the open flash-point and firetest of lubricating oils, but the close flash-point is also usually ascertained, a modification of the Abel or Abel-Pensky apparatus, known as the Pensky-Martens, having been devised for the purpose.
In civilized countries provision is made by law for the testing of the flash-point or fire-test of lamp-oil (illuminating oil or kerosene), the method of testing and the minimum limit of flash-point or fire-test being prescribed (see below, Legislation).
The invention of the apparatus, legalized in 1879, for the determination of the flash-point of petroleum, was another piece of work which fell to him by virtue of his official position.
Since the inception of the petroleum industry, most civilized countries have prescribed by law a test of flash-point or inflammability, designed in most cases primarily to afford a definition of oils for lighting purposes which may be safely stored without the adoption of special precautions.