The test with regard to spontaneous combustion is one which ought on no account to be overlooked. It has no relation to what is termed the "flashing-point " of an oil. Scientific investigation seems to show that oils which have a viscid character are those which possess, in varying degrees, the dangerous property of setting up a high degree of heat under certain circumstances. So far as the flashing-point is concerned, the most volatile of natural lubricating oils will not give off an inflammable vapour at a lower temperature than 200° F. (93° C). Consequently the vapour cannot come into play until danger presents itself from some other source. As for the risk of spontaneous combustion, the following test has been applied:- Cotton waste, soaked in Ran-goon engine-oil, was enclosed in a metallic vessel surrounded by an air-bath having a temperature of 170° F. (77° C.}. In 6 1/2 hours the temperature of the oiled cotton had not risen to above 144° F. (62° C). The gas flame which heated the air-bath was allowed to remain under the vessel for a further period of 17 hours, but no change was produced, except that there was discernible a slight smell, due to the evolution of acrid vapour in small quantity,' arising from the slow decomposition of the vegetable part of the oil.

The bath was next raised to 190° F. (88° C), and so remained for 24 hours; but no effect was produced. The temperature of the bath was next raised to 200°; F. (93° C), and left at that point for 6 hours, but the material still remained perfectly quiescent, showing its utter incapability . of producing spontaneous combustion.

In contrast with the foregoing, it may be mentioned that cotton soaked with olive-oil (Gallipoli), on being exposed to a temperature of 170° F. (77° C.) for a day and a night, was found, on examination in the morning, to be much charred, the centre portion being reduced to ashes, showing that actual ignition had taken place. In a series of experiments conducted by John Galletly, a quantity of cotton waste was soaked in Gallipoli olive-oil, and loosely packed in a paper box, in size about 1/16 cub. ft. The box was exposed to a temperature of 130° F. (54° C). Two trials were made under similar circumstances. In the first, rapid combustion was found to be coming on in little more than 5 hours, and m the second within 6 hours. Remarking on these and similar experiments with other oils (exclusive of the hydrocarbons), Major V. IX Majendie, R.A., Her Majesty's Inspector of Gunpowder Works, observes:-"These facts illustrate the grave and urgent character of the risk which exists when oiled cotton waste is deposited, even in very small quantities and for a very short space of time, in moderately elevated temperatures-such temperatures as exist in the majority of factories, in the neighbourhood of a steam-pipe, or under exposure to the sun's rays."

One of the most delicate articles to lubricate is a watch, and special precautions are necessary to be observed in selecting a material, or combination of materiab, for -this purpose. Some find porpoise-oil to give most uniform satisfaction, though perhaps rather thin for certain parts. To get rid of acid in the oil, the latter should be washed in filtered water, to which a little soda carbonate has been added; after settling, the oil is poured off, and heated to 212° to 225° F. (100° to 107° C.) for an hour or so with constant stirring. The plan of placing lead shavings in oil to neutralize the acid, is thought by some to exert a drying influence. Oil cannot be tested for acidity by the direct application of litmus; but filtered water used for washing the oil will redden litmus-paper if any acid was present in the oil. Crisp thinks that no very fatty oils (neatsfoot, lard) will repay the trouble of washing and refining; and he is of opinion that all oils refined by heat, by evaporation, by alcohol, or by any quick method, though looking clear and bright, have their lasting properties quite destroyed.

He declares it is only by a slow process of abstracting the deposits from the oil at 30° to 32° F. (-1° to 0°C.) that a reliable oil can be obtained suitable for watchmakers. Vaseline may be used with great advantage in the priming up of fusees; a small quantity may also be applied to the collet. Oils for chronometers or watches ought (1) to be chemically pure, (2) not to gum or clog, (3) not to evaporate, (4) not to freeze. Before refining, sperm-oil gums; olive-oil is acid, and discolours steel and brass, which acidity is much reduced or annihilated by the washing process; neats-foot-oil is very hard to get genuine. Rarely can the oil be depended upon that is offered in the market; besides, neatsfoot is a very tender oil, and requires to be filtered at a very low temperature to get rid of the stearine. As an instance of this, a gallon obtained perfectly genuine was quite solid at a temperature of 50° F. (10° C). Upon putting this gallon into a bag, about 1 qt. filtered through the bag at a temperature of 32° F. (0° C), which is the only portion suitable for watchmakers, and this portion requires washing and again filtering to get rid of its acidity.

This is also about the proportion that can be obtained from olive and sperm oils, yielding about J, or 1 qt. per gallon, under the same conditions of obtaining oil under the cold process.

Some hundreds, if not thousands, of formulae have been propounded for the fabrication of lubricants suited to all needs; the following are selected as examples:-

(1) English railway axle-grease.

(2) German railway-grease.

(3) Austrian railway-grease.

(4) French lard. Dissolve 3 oz. shredded indiarubber in 1 gal. finest rapeseed-oil by the application of heat.