Close and open flash. points and fire-test.

Pensky.

Martens tester.

Description of the

instrument.

as far as practicable, been adequately cleansed and ventilated and rendered free from risk of explosion or fire. If from any cause a complete certificate of this sort cannot be given, then it should be clearly notified which tanks or spaces have not been cleansed and are still dangerous."

This recommendation has been generally acted upon, and such certificates are now given.

16

Lubricating Oils. In this country it is customary to determine the close and open flash-points and firetest of these oils. The two latter may be ascertained by heating the oil at the rate of 10° F. per minute in a porcelain crucible about two inches in diameter, which is filled with the sample to be tested to about a quarter of an inch from the top and placed in a sand-bath, a gas-flame inch in diameter being passed across the surface, on a level with the edge of the crucible, at each rise of two degrees of temperature, indicated by a sensitive thermometer, the bulb of which is immersed in the oil, until a flash takes place, and subsequently, on further elevation of temperature, the oil ignites and continues burning. The more usual practice, however, is to test the oil in a special form of apparatus, and, having determined the close flash-point, to remove the cover of the oil-cup and proceed to ascertain the open flash-point and fire-test by using a test-flame in the manner described.

The apparatus most largely in use is that known as the Pensky-Martens tester, which is shown in Fig. 13, with the test-flame in position for igniting the vapour; the cover of the oil-cup being shown in plan and side view, and a handle, for removing the oil-cup, in the separate figures.

The cover of the oil-cup consists of two parts-viz., the portion joined to the rim, and an upper portion which revolves through a small are. In each portion

there are three orifices, the central one being twice the area of the two lateral ones. These orifices may be made to coincide, or the openings may be completely closed, according to the relative positions of the two portions of the cover. The lower part of the cover is fitted with a vertical rod serving as a support to a tube. This tube can be rotated upon the rod by turning the

Fig. 13.

non-conducting milled head at the upper end, and the action compresses a spring. At the lower end the tube is provided with an arm which, by the action of the spring, is held against a vertical stud. A pin projecting downwards from the arm engages with a slot in the revolving portion of the cover, and on turning the milled head the openings in the upper portion of the cover are brought over those in the lower portion. At the same time, a flange projecting from the edge of the

Rate of

heating.

revolving portion of the cover comes into contact with
the oscillating test-jet, and this is depressed, so that at
the same moment when the central openings coincide,
the test-flame is brought to the orifice. On releasing
the pressure requisite to turn the milled head, the
openings in the cover are again closed by the action of
the spring, and the test-jet is brought back to the hori-
zontal position by the weight at the opposite end.
This weight is attached to a stem forming a screw
valve, by means of which the size of the test-flame can
be adjusted. The gas is supplied through a lateral
tube forming one of the supports on which the jet
oscillates, the other support consisting of a small stud.
In the lower part of the cover of the cup there is a
socket for a thermometer, and in the centre of the
cover there is a tube through which the stem of the
stirrer passes. This stirrer is provided with a pair of
arms working in the oil, and a smaller pair in the
vapour-space above the oil.
It is revolved by means of
a flexible wire stem. The oil-cup is furnished with a
pair of hooks for convenience in removing it from the
bath when hot by means of the forked holder shown.
The heating-vessel consists of a cast-iron air-bath with
an annular chamber exposed to the flame, and a brass
jacket, which serves to check radiation. The jacket is
separated from the iron casting by a considerable space
at the sides and by a distance of a quarter of an inch
at the top. The oil-cup rests upon the jacket, and
therefore does not come into contact with the cast iron.
Beneath the bath there is a disc of wire gauze which is
fitted to a swinging arm, so that it may be turned
aside and the flame of a Bunsen burner allowed to
impinge upon the bath when a high temperature is
required.

The flame of the burner may be regulated so that
the temperature of the oil rises at the rate of about

L

10° F. per minute. In employing this or any other form of close-test instrument in the testing of lubricating oils, it is important that the samples should be Freedom of

free from water, as the presence of aqueous vapour in sample from

water essential.

Fig. 14.

Fig. 15.

the upper part of the cup prevents the occurrence of the" flash."

tester.

Figs. 14 and 15 show Gray's instrument for deter- Gray's mining the flash-point of heavy oils. The apparatus consists of a brass oil-cup of the same dimensions as

Substitute

for gas.

Directions

for use.

that employed in the Abel instrument, supported on a
tripod stand and covered with a tight-fitting lid
through which passes a steel shaft carrying on the end
within the cup two stirrers, one for the oil and the
other for the vapour.
The upper end of the shaft
terminates in a bevelled wheel engaging with another
similar wheel on a horizontal shaft supported by two
bearings and rotated by a handle fixed in an ebonite
disc on its further extremity. This shaft also carries
a collar from which project two pins at diametrically
opposite points. These, when the shaft is drawn out a
little way so as to disengage the bevel wheels, come
into position for applying the test-flame. In the lid
are three openings-one immediately in front of the
test-flame, and the others on either side of it. The
sliding cover is pierced with two orifices corresponding
to those on the lid, and is kept closed (as shown in
Fig. 15) by a spring while the bevel wheels are in

gear.

On drawing back the shaft, one of the projecting pins engages with the horizontal arm of an upright rod connected with the slide, which is turned round when the handle of the shaft is moved about a quarter of a revolution, the openings in the lid being thus uncovered and the test-flame simultaneously applied. Where gas is not available for the test-flame, a good substitute is obtained by passing a current of air or hydrogen through cotton wool or other absorbent material saturated with gasoline.

The following are the directions for use prescribed by the inventor: The oil-cup being filled up to the mark inside with the oil to be tested, the thermometer is placed in its socket and heat is applied either by a direct flame or by the interposition of a sand-bath. The test-flame is adjusted to a diameter of about oneeighth of an inch. During the heating the stirrers should be rotated at short intervals, and in proportion