This may be secured by using a large water-bath to surround the apparatus, but in experiments of long duration it is necessary to use an accurate temperature regulator.
The solution obtained is neutralized, concentrated on the water-bath, acidified by sulphuric acid and extracted with ether.
The earliest form of testing instrument employed for this purpose was that of Giuseppe Tagliabue of New York, which consists of a glass cup placed in a copper water bath heated by a spirit lamp. The cup is filled with the oil to be tested, a thermometer placed in it and heat applied, the temperatures being noted at which, on passing a lighted splinter of wood over the surface of the oil, a flash occurs, and after further heating, the oil ignites.
The German investigators seem to have a great preference for the H form of cell, but it is clear that a narrow tubular cell of the British board of trade form not only comes more quickly to the temperature of the water bath in which it is placed, but is more certain to be wholly at one temperature.
Surrounded By A Nickel Plated Steel Enclosure B, Forming The Bulb Of A Mercury Thermo Regulator, Immersed In A Large Water Bath Maintained At A Constant Temperature.
