an apparatus, Fig. 126, constructed by Engler,* which is based upon the principle as the apparatus used in the lubricating oil factories at Baku.

Steam generated in a small boiler is superheated in pipes to about 572° F., and to maintain it at uniform temperature is conducted into the copper receiver R, which is provided with a screw-lid made tight by an asbestos ring. In this lid are screwed the tube for the reception of the thermometer d, also the small cock t, through which in the beginning of the operation the air is discharged, and the steam when the operation is finished. The cock serves for discharging the condensed water. By heating upon a small gas-stove the temperature of the steam passing through R is maintained at 572° F. The steam passes through a pipe covered with asbestos paper to B, and from there into the oil through the pipe b, which is provided with numerous small holes directed downward at an angle of 45°. The copper still B is about 734 inches deep and 734 inches in diameter, and holds about 6.6 to 8.8 lbs. of oil (it may be made of any size desired). Upon it is screwed. a helmet, also rendered tight by means of an asbestos ring. The temperature in the still is indicated by the thermometer v in the tube v'. The still B being filled with oil, it is slowly heated upon a gas stove. With too rapid heating the oil, if water is present, runs over very readily, and strong bumping takes place. A more energetic heat should be applied only after the thermometer v shows a temperature of 266° F. When a tem

perature of 572° F. has been attained, the steam heated to 572° F. is introduced from R into the still by closing the cock t, and the vapors are conducted into the separatory condenser S joined to the helmet by the connection c. This condenser consists of copper pipe bent three times. It has a diameter of about 1⁄2 inch and a total length of about 5 feet, each bend being about 934 inches long. Into the bottom of each bend is screwed a small discharge-pipe 0, 0, 0, which to cool the distillates are placed in a vessel filled with cold water. With the separatory condenser is connected a condensing coil K cooled by water. This serves for condensing the rest of the vapors, especially the steam. The neck of the helmet and the separatory tubes should be covered with asbestos paper to prevent the condensation of light oils and water in them.

In the commencement of distillation light oils and a small quantity of water condense at 5, $1, $11. These are removed and combined with the distillate from K. However, in the course of 15 to 25 minutes distillation progresses regularly and the heaviest and thickest oils condense in the leg s and thinner oils in s, and s,,, while the lightest oils together with steam pass into K. It is a characteristic feature of this process that thick oils immediately separate in the commencement at s, which is a clear proof that a sufficient separation can never be effected by the ordinary method of fractional distillation, in which in the beginning light oils and then oils becoming constantly heavier are caught; besides, the first so-called light distillate contains a considerable quantity of heavy oils, which in Engler's apparatus are separated in s or s,.

By this method four fractions are thus obtained, which are weighed, whereby the content of the different light and other parts is established.

Flashing Point.

Petroleum consists of a mixture of hydrocarbons and with a preponderance of light volatile oils its use is dangerous. When the readily volatile oils are not sufficiently separated by distil

lation, petroleum frequently evolves vapors even at the ordinary temperature of a room, which form, with the air in the oilholder of the lamp, explosive gas mixtures. According to Chandler's experiments the most violent explosion occurs with a mixture of I part petroleum vapor and 8 to 9 parts air; I part air and 3 parts petroleum vapor give a slight report, while a mixture of 1 part air and I part petroleum vapor does not explode. According to Thörner, the explosive mixtures contain at least 1.9 to 3.2 per cent. by volume of petroleum hydrocarbons. To what degree a few per cent. of naphtha reduce the degree of temperature at which the oil evolves inflammable vapors, is shown by the following experiments of Dr. C. B. White, of New Orleans, Louisiana. With an oil which originally yielded inflammable gases at 113° F., the respective degrees of temperature fell with the addition of I per cent. naphtha to 103° F.; with the addition of 2 per cent. naphtha to 92° F.; with the addition of 5 per cent. naphtha to 83° F.; with the addition of 10 per cent. naphtha to 59° F.; with the addition of 20 per cent. naphtha to 40° F.

The property of petroleum to evolve on heating inflammable vapors which explode when mixed with air is called inflammability, and the degree of temperature at which vapors are evolved in sufficient quantity to allow of their ignition, the flashing point. The lower the latter is, the greater the danger in using the oil in lamps or stoves.

By combustion is understood the property of petroleum to take fire and continue burning when heated to a certain temperature, and the lowest temperature at which it will take fire is called the burning point. Hence, a distinction has to be made between the flashing test and the burning test. These two tests are often confounded. In the first case, only the vapor over the oil burns or explodes, the combustion not extending to the oil itself; in the latter case, the ignition of the vapor is transferred to the oil itself, the latter continuing to burn on the surface. The burning point and flashing point, therefore, can never agree, and, in fact, the burning point of an

oil may be from 10° to 70° F. higher than the flashing point. In ordinary petroleum the burning point is, as a rule, from 41o to 53° F. higher than the flashing point.

The flashing test is the most important test, as it is the inflammable vapor evolved at atmospheric temperature that causes most of the accidents. Moreover, an oil having a high flashing test is sure to have a high burning test, while the reverse is not true. In most countries regulations regarding the minimum flashing point permissible have been established. In making such regulations the degree to which the oil in the burning lamps is heated above the surrounding air must, of course, be taken into consideration. Chandler, in his experiments with 23 lamps and 72 varieties of petroleum, found that during seven hours, with the air of the room at from 73° to 74° F., the temperature of the oil in the burning lamps ranged from 76° to 100° F., the highest temperature of 100° having been reached in a metal lamp at the end of one hour. That this was an exceptionally high temperature is shown by the fact that the highest temperature reached in any other lamp was 92° F. With the air of the room at from 82° to 84° F., the temperature of the oil in the burning lamps ranged from 82° to 120° F. The temperature 120° was exceptional, being confined to one lamp. With the air of the room at from 90° to 92° F. the temperature of the oil in the burning lamps ranged from 84° to 129° F., the highest temperature being exceptional.

From these results it appears that the temperature of the oil in burning lamps often rises much above 100° F., thus reaching a temperature at which oil which does not emit a combustible vapor below 100° F. would be dangerous.

Apparatuses.

The large number of apparatuses constructed for determining the flashing point may be divided into two groups, those of the first group being based upon the principle according to which the expansion of the vapor which the petroleum shows at fixed temperatures is measured. In the apparatuses of the second

group the petroleum is heated in a vessel to the point at which the gases accumulated over the oil can be ignited or exploded by bringing them in contact with a small flame.

1. Apparatuses in which the expansion of the vapor is measured.

The Salleron-Urbaine apparatus may be designated the most complete of this kind. It consists of a brass or copper vessel A, Fig. 127, in which is fixed the conical pillar D, and which is covered by the plate d d, fitting on its upper edge. C is a movable plate turning on the pillar D, and held in place by the

screw n. In this movable plate is the cylindrical chamber B, closed at the top by the screw-plug p, while its lower opening can be placed in communication with the vessel A, by means of the opening o, or, by turning the plate c, it can be sealed by the upper surface of d. There are also in the plate d, a thermometer, a graduated tube m, 35 centimeters (13.78 inches) long, and the regulating apparatus, which consists of the