This section is from the book "The Principles And Practice Of Modern House-Construction", by G. Lister Sutcliffe. Also available from Amazon: How Your House Works: A Visual Guide to Understanding & Maintaining Your Home.
The illuminating: power of candles is subject to great variations, owing partly to their mode of construction, and also to the great irregularities caused by the lengthening and shortening of the wick; thus, when a freshly-snuffed candle is first lit, there is a rapid increase in the power of the light, and this increase continues until the burnt wick leaves a residue of waste and spongy matter, from which all combustible material has been extracted. This, if not removed by snuffing, will cause the light to decrease as steadily as at first it increased. Such variations in the burning intensity of candles have been found by experiment to reach the following almost incredible ratios: - A candle which, when first lit. gave an intensity of 100. gave in four minutes about 90, and in twenty minutes only 30. It can be seen from this that such an illuminant cannot be handled, for the Bake of comparisons and experiments, with the same facility with which we can treat lights of a more regular character. Hence, beyond its use as a mere verbal standard of power, we may dismiss this form of lighting altogether.
By E. A. Claremont. Number Of The Institution Of Electrical Engineesr ; Member Of The Instituton Of Mechanecalcal Bttaarom Aituor Or "Election Lighting", Etc.
In England, however, as the expression "candle-power" (C.P.) has reached a somewhat similar position in the comparison of intensities of light to that possessed by Carsel's lamp in France, I may as well state here that this standard was originally derived from a spermaceti candle, consuming 120 grains per hour, and that all relative tests are made, not directly by measuring the relative intensities of the flames, but by gauging the relative depths of the shadows thrown by them.
Mineral burning: oils, usually purchased under such names as "Daylight", "Sunlight", "Kerosene", etc., are formed from the differently-refined products of petroleum and shale oils. By "petroleums" are usually meant such oils as are obtained from springs, in their crude or liquid form, while the shale products are those distilled from oil-producing turf and rocks; although the word "petroleum" is usually applied to the former, and "paraffin" to the latter, we may really look upon these names as mere British trade-distinctions. The word "kerosene", which was formerly used to distinguish a particular brand of Russian oil, is now applied to mineral burning oils generally, at least to such of them as are suitable for burning with wicks. Kerosene is a colourless liquid, insoluble in water, lighter than water (upon which it will therefore float), and usually possesses a well-defined blue fluorescence. Good kerosene may also attain a yellowish tint, but this should not be too pronounced, as it would point to the presence of heavier oils, which, to be consumed satisfactorily, would require a wick of looser texture than that employed for the finer samples. It should be noticed, however, that the yellow appearance may be caused simply by undue exposure to light.
In England, all Government requirements, regulating the storage, transportation. etc., of burning oils, are regulated by what is known as their "flashing-point". This is simply the degree of heat at which the oil begins to give off sensible quantities of inflammable vapour. This method of deciding the inflammability of oil is far superior to the method still much in vogue in America, where the "burning-point", or temperature at which an oil ignites bodily, is considered sufficiently reliable for ordinary purposes. As, however, the burning-point depends very largely on surrounding circumstances, - such as the pouring of the oil over a broad porous surface, when it will ignite much more easily, - such a standard gives little idea of the nature of the oil.
In the case of cold kerosene, neither the oil nor its vapour ignites on the application of a light. In the case of lamp-explosions, such vapour must have been given off at a higher degree of temperature than the flashing-point of the oil (probably through heat conducted by the body of the lamp), when, of course, such vapour becomes explosive. In England, as the result of numerous eom-parative experiments made with two forms of apparatus, of which that known as the "close test" is the one usually employed, the flashing-point of " petroleums", as kerosenes are termed in the statute-book, has been fixed by law at 73° Fahrenheit. This standard, though considered by some to be too fine owing to the best of the American oils being kept for home consumption, does not really affect the better qualities of the kerosene imported into this country, of which the flash-point is not usually leas than 100* to 120*
Russian oils give a steadier light than American, as they do not seem to possess the same mixture of light and heavy constituents, which usually cause the American oils to burn at first with their greatest brilliancy, gradually diminishing as the oil in the reservoir decreases and the- heavier portion is reached. Russian oils, however, though steadier, never give as much light.
Owing to such variations in the density of kerosenes, it will be seen that great care should he exercised in the choice of wicks, for, especially in the case of the heavy oils, a wick of loose and pliable texture, such as is generally made from long staple American cotton. is infinitely preferable to others of a harsher nature.
In the consideration of oil-burning as an illuminant, we enter upon the most dangerous phase of lighting. From the most recent experiments by experts, it would seem that, from a representative collection of ordinary oil-lamps purchased in England and subjected to rigorous tests, those considered as dangerous or unsafe readied the extraordinary total of 90 per cent of those bought. From the list of casualties published by the Public Control Department of the London County Council, we see that in 1894 the fire-brigades were called to no less than 44S tires in the metropolis alone, all of which were ascribed to oil-lamp accidents, of this number 337 were caused by the upsetting of lamps, while only 90 were brought about by explosions. Thus it seems that, in the use of oil-lamps, the danger most to be feared is that occurring through the leakage of oil from the reservoir after upsetting, and this we find from the most recent statistics is caused by lamps being built of fragile material, burners being attached by screws whose threads are of an imperfect nature (or on which there are no threads at all), and by sconces holding wieks of imperfect fit, thus allowing an outlet through which the oil may flow. On the other hand, explosions, which would seem to be of much less frequent occurrence, are chiefly caused through the vapour in the reservoir becoming inflammable, on account of the temperature of the oil having exceeded its flashing-point, this being generally due to heat being conducted through the body of the lamp from the burner. It would seem, therefore, that the material of which the reservoirs are composed should be of non-heating capacity, but as this would result in their being constructed either of glass or porcelain, it would lead to a worse evil, namely, having an apparatus of a fragile nature.