measured off in the measuring flask C and poured into the vessel A, which thereby should be filled exactly up to the marks c. The temperature of the water is then brought to 20° C. (68° F.), this being done by maintaining the water or heavy mineral oil in the jacket BB at a uniform temperature until the thermometer t shows exactly 20° C. (68° F.) and the thermometer fixed in B differs but slightly from it. The measuring flask C having in the meanwhile been allowed to drain off for at least one minute, is then placed under the orifice, the hard wood stopper b withdrawn, and the time in seconds noted by a watch or chronometer which is required for the measuring flask C to be filled up to the 200 cubic centimeter mark. Before allowing the water to flow care must be taken that it is perfectly still and especially not in a rotatory motion due to previous stirring. If the apparatus is properly constructed 50 to 55 seconds are required by the water to run out. The mean of at least three determinations, which should not vary more than 0.5 second from each other, is however taken as the correct figure and placed 1. Very exact determinations should be executed in a room having as nearly as possible a temperature of 20° C. (68° F.).

In testing oils care must be taken to remove every trace of moisture from the vessel A, this being effected by drying and rinsing in succession with alcohol, ether and petroleum. The apparatus is finally rinsed with the oil to be tested and then filled with the latter up to the marks c (only thin oils can be measured like water in the measuring flask C). By heating the mineral oil-bath the temperature is then brought to the degree desired, and maintained at that degree for at least three minutes before allowing the oil to be tested to run out. The time required for the oil to run out is determined in the same manner as described above for testing the apparatus. The figure obtained, for instance, 270 seconds, is divided by the figure of the flow of water of 20° C. (68° F.) in the same apparatus, for instance, 52 seconds, which gives the so-called specific viscosity or degree of viscosity, hence, in this case,

Oils containing particles or water in suspension have to be passed, before testing, through a dry filter. Instead of water, rape oil may be taken as the unit in testing lubricating oils, but water only in testing petroleum.

After a number of experiments with Engler's viscosimeter in the technical experimental station at Berlin, the conclusion of this being the most suitable apparatus has been reached.

Lepenau's leptometer. This apparatus, shown in Figs. 161 and 162, allows of a direct comparison of the viscosity of the oil

to be tested with a standard oil, generally rape oil, under the same conditions, two oil-holders, one of which is filled with the standard oil and the other with the oil to be tested, being combined in one bath, and the oils passing out simultaneously through two tubes of the same shape. A is the bath in which the two oil-holders B B are so placed as to be surrounded on

all sides by the fluid in the bath. For this purpose the partition between B and B is open on top and below, so that the fluid can circulate in it from a. The two oil-holders B B are connected below by means of pipes with c c, whence the oil, by three-way cocks, passes into a pipe in which outflow-orifices d d of different diameters, according to the consistency of the oil, are inserted; t t are thermometers, the bulbs of which dip into the oil passing through c, and ƒ are rising pipes for the removal of air bubbles. Through g the oil can be directly discharged from B B, and by adjusting the three-way cock the oil can be run off through d or through g; or finally B can be shut off. In making experiments, a is filled with a fluid for heating purposes. One of the vessels B is filled with standard oil and the other with the oil to be tested, and after heating to the desired temperature, both oils are allowed to run off simultaneously through the orifices d d. The relative viscosity of the oil to be tested, as related to the standard oil, is then directly found from the volumes or weights of the oils run off.

At the ordinary temperature this apparatus gives very good results; it has, however, the defect that in consequence of the outflow-orifices not being in the heating bath, the oils in them will cool off several degrees, according to the surrounding temperature. The construction of the different outflow-orifices with perfectly uniform internal dimensions might also prove difficult; the outflow-orifices should at least not be bent as in the most recent constructions, they being difficult to clean and keep in order.

Prof. Stefano Pagliani's viscosimeter "for the determination of the internal friction of very viscous fluids." The apparatus consists chiefly of two parts, a pressure-reservoir for the production of the pressure required for the flow, and the outflowvessel.

A metallic stand carries on its lower end a metallic receiver which is connected with the outflow-vessel, while the necessary pressure in the latter is produced by a vessel filled with water placed at a higher level. The outflow-vessel, the actual

viscosimeter, consists of three parts, two graduated vertical glass tubes of special shape and a horizontal tube which connects the two vertical tubes. The vessel stands in a box which is heated.

One of the vertical tubes is filled with the oil to be tested, and after the temperature desired has been reached, air is forced upon the oil, whereby the latter rises in the other vertical tube. After establishing the outflow-time T, the pressure and the volume v of the oil run out, the viscosity is determined according to the formula.

"=KPT (K being the constant). The apparatus is said to be successfully used by the "Societa delle ferovie delle Rete Mediterranea."

A. Marten's viscosimeter. This apparatus is shown in Fig. 163. The vessel A is placed upon a trevet in the air-bath formed by the double-sided box B with a solid back glass wall

D and a movable front glass disk. The air-bath can be heated by the burners E by means of the side-chambers F. The thermometers T and H indicate the temperatures of the airbath and the oil. The stirrer K of platinum wire serves for

agitating the oil in order to uniformly distribute the heat. The vessel A and the flask C are provided with marks for measuring the oil. The stopper G of the flask C reaches through the cover of the air-bath so that it can be withdrawn from the outside. The heat can be readily regulated by the flame and by from time to time opening the glass wall. This arrangement has the advantage over an apparatus with oil-bath that the oil which has run out is not cooled off and that the apparatus can be readily cleaned.

B. Redwood's viscosimeter. This apparatus has been adopted by the Scotch Mineral Oil Association. The result is expressed in minutes and seconds required by 50 cubic centimeters of oil to pass through the tube of the apparatus at 21° C. (69.8° F.)

Testing the viscosity by means of the inclined plane. An apparatus for thus testing oils is illustrated in Fig. 164. It con

sists of a piece of plate-glass set with considerable inclination. and heated by means of a vessel of boiling water to about 200° F., and held at a uniform temperature as indicated by the thermometer attached. A drop of oil placed at the top will flow down. A scale on the side affords a convenient means of