These figures may express the chemical effect of these oils upon brass, and thus give values for the estimation of these oils as protectors of metals; to form estimates of their values as lubricators, the above obtained factors will doubtless prove valuable, but the mechanical action in friction will have also to be considered. These figures also express merely results obtained with the oils under investigation, as the acidity of the vegetable and animal oils differ. Probably the results of their effects upon metals will differ; but in general it may be stated that these oils in course of time will invariably show acidity; and in this respect only mineral oils are excepted. (Oil and Paint Rev.)

The lubricating power of a mineral oil increases with its specific gravity. Wherever, therefore, in machinery there is great friction with heavy pressure, only heavy mineral oils should be employed, and if they are properly prepared- i.e. free from resins and acids-: they retain their lubricating power at any temperature. Animal' and vegetable oils, on the contrary, however pure, gradually lose this power, and, owing to the oxidizing action of the air, become thick, gummy, and eventually quite stiff, and hence continual oiling and frequent cleaning become necessary. The heavy mineral oils have not this tendency to become thick under the same influences. Then, again, at a low temperature, animal and vegetable oils become thick, or even solid, whereas mineral oil always remains liquid, and even the greatest cold only makes it slightly thicker, but never solid. The chief advantage, however, of the mineral oils is that they do not act upon iron like those of animal and vegetable origin. As already stated, the latter are composed of fatty acids and glycerine, a combination which is broken up into its constituent parts by superheated steam. (On this fact the manufacture of stear-ine and glycerine depends.) The same decomposition, however, takes place, although only gradually, under the influence of atmospheric moisture even at the ordinary temperature.

The free fatty acids attack the metals with which they are in contact, forming the so-called metallic soaps, and this takes place irrespective of the presence of .steam. The affinity of the fatty acids for ferric oxide is indeed so great, that it seems as if the iron dissolved in them at the moment of contact. (Leip. Farb. Zeit)

During experimental observations on paraffin-oils, it was found that certain oils burned somewhat imperfectly in different lamps, and an examination of these oils led to the discovery that they were contaminated so largely with lead compound as to lead to the choking up of the wicks, and ultimately to the lessening and practical extinguishment of the light. In the case of one of the oils, the wick of the lamp had to be changed several times during a single night,, and the examination of. these wicks proved that they contained so much lead compound as to leave, when charred, a fine network of metallic lead. The oil in question had been stored in a cistern or tank lined with sheet-lead, and notwithstanding the absence' of affinity between paraffin-oil and other substances, as indeed its own name indicates, the oil had apparently acted upon the metal, and held the lead in solution. In order to determine how far paraffin-oil could act upon lead, a series of experiments was instituted, in which oils of various qualities, originally free from lead, were allowed to remain in contact with the metal for different periods of time.

These experiments proved that all the samples of paraffin-oil which were experimented upon had more or less action upon metallic lead; that mere contact of the oil with the lead was sufficient to communicate traces of lead to the oil; and that in a week's time the oil invariably became so highly charged with lead that it was rendered unsuitable for combustion in ordinary lamps, owing to the encrusting of the wicks, and the consequent lowering of the luminosity of the flame. In order to render the experimental observations more complete, similar trials with paraffin-oil and other metals were carried on; and to enable the various experiments to be compared with each other, the same quality of oil was employed in the principal investigations with the different metals. Twelve series of experiments were made with the highest quality of burning-oil and the metals-lead was employed in 3 of the trials because this metal is more liable to be acted upon when the surface is bright than when the surface posr sesses the ordinary skin or coating of oxide and carbonate, and the results obtained with bright lead might not apply to tarnished lead.

This difference in action is well known in the case of the chemical influence of different natural waters upon lead.

(1) Bright Lead

When paraffin-oil is brought into contact with scraped lead, where the surface is quite bright, the chemical action begins instantly, and a few moments are alone required to communicate the metal to the oil. In a day the action is.so decided that the oil begins to present rather a cloudy appearance, owing to the presence of the; lead compound; and on washing the oil with water, the latter when settled retains a milky appearance from the lead compound, which is apparently a basic salt, and has an alkaline action on test-papers. (2) Tarnished lead with unprotected edges.-Lead cut into small sheets and placed in the paraffin-oil, without any protection to the freshly cut edges, necessarily exposes a large surface of tarnished metal with the natural skin of oxycarbonate, and a comparatively snail surface of bright metal, where the fresh-cut edges are visible. The investigation showed that under these circumstances the lead is not so readily acted upon by the oil, but in a couple of days the oil gets impregnated with lead compound, and becomes unsuitable for illuminating purposes. (3) Tarnished lead with protected edges. -In this case the lead was taken with its natural skin,. and the freshly cut edges were protected by wax.