208 



THE POPULAR EDUCATOR. 



feeble light. The movement of the air past the flame is also 

 well shown. The ascending current drags the flame out to a 

 pointed figure, and, whilst rushing past the candle, keeps the 

 outside of the cup containing the melted wax or tallow cool, j 

 The air that rushes by so quickly burns up the carbon and 

 hydrogen of the outer part of the flame, but does not affect so 

 materially the next structure, where the hydrogen is chiefly 

 burnt and the carbon deposited. Here the flame is the brightest, 

 because .of the ignition of the precipitated carbon, and hence 

 the reason that the shadow of this portion should appear so dark. 

 In the inner layer the unburned gas is found waiting its turn to 

 pass to the exterior, to go through the phases of partial com- 

 bustion and precipitation of the carbon, ending with complete 

 combustion at the exterior. 



That the interior of a candle flame does consist of unburnt 

 gas may be shown by placing a narrow glass tube in the inner 

 cone of the flame. The tube must be inclined, and if nicely 

 managed the hot gas passing upwards may be inflamed at the 

 top. The same fact is shown by holding a slip of card across 

 the flame. The interior of the cone does not scorch the card, 

 which is blacked at the two points or opposite sides of the centre. 



The tube may be adjusted so as to draw away the finely- 

 divided carbon deposited in the luminous portion of the flame, 

 and if this is conducted into a separate small hydrogen flame, the 

 latter .becomes luminous in consequence of the incandescence of 

 the carbon derived from the candle. A hydrogen flame affords 

 little or no light, but if a small bit of tow, saturated with 

 benzole or ether, is placed in the bottle containing the materials 

 for generating hydrogen, and the tube or jet fitted into the 

 neck of the bottle, on lighting the hydrogen it is now very 

 luminous, in consequence of the carbon, the solid matter de- 

 rived from the benzole or ether, being precipitated, ignited, 

 and burnt. To distinguish the bright from the almost un- 

 luminous part of the flame, the latter is sometimes called the 

 mantle, because it is the outermost cone. 



The best method of showing the structure of flame is to 

 place some ether in a tin dish three inches in diameter and 

 half an inch high. On setting fire to the ether a very large 

 flame is produced, and into its centre may be introduced a cup 

 containing phosphorus, which only sublimes, but does not burn. 

 By very careful manipulation, and when the air is still and not 

 disturbed by open doors or windows, gunpowder may be dropped 

 down a tube held across the hot stratum, and will fall unburut 

 into a porcelain or other cup, placed in the centre of the flame. 

 A very few grains of powder should be used until the operator 

 has sufficient confidence to perform the experiment steadily. 

 The structure of flame being understood, it is easy to see how 

 the illuminating power of an ordinary flame may be increased 

 by admitting the right proportion of air to the interior. The 

 argand burner furnishes the best illustration of this well- 

 known principle : if the central tube is corked and the chimney 

 removed, the flame is smoky and unsteady; on replacing the 

 chimney, the current of air rushes with increased velocity past 

 the exterior, and more light is obtained ; but the maximum of 

 iight is only procured when the cork is removed, and air allowed 

 to pass to the interior as well as the exterior of the flame. 



When the supply of air is too great, the luminosity of the 

 argand burner is seriously affected, especially if the gas is not 

 rich in hydro-carbons, because the carbon is burnt up at once, 

 and no time is allowed for its precipitation ; hence it is now usual 

 to adjust the central or internal tube of the argand burner to the 

 quality of the gas. The diameter of the internal aperture 

 fihould be less than half an inch viz., 0'42 of an inch for eleven- 

 candle gas, and half an inch for fifteen-candle gas, if used with 

 a, glass chimney seven inches long, and burning at the rate of 

 five feet an hour. 



If coal-gas is mixed with a considerable quantity of air 

 before it is burnt, as in a smokeless burner, or the gauze-burner, 

 the flame is no longer brilliant, because the carbon is burnt with 

 the hydrogen. 



When the combustible oil, such as turpentine or camphine, 

 contains a very large proportion of carbon, the chimneys are 

 increased in length, and have a peculiar construction, because 

 more air must be supplied to burn the excess of carbon, and to 

 prevent the flame smoking. 



The Bude light consists of a small argand lamp, burning 

 colza oil ; and instead of supplying air to the interior tube, a jet, 

 conveying oxygen gas from a bladder or snail indiarfnibber bag. 



is attached ; the smoky flame immediately burns most brilliantly, 

 and if the wick is very thick and the oil good, it will afford a 

 considerable amount of light. 



It is a curious fact that when the pressure of the air is re- 

 duced the luminosity of a burning candle is materially affected. 

 Messrs. Tyndall and Frankland burnt some candles on the 

 summit of Mont Blanc, and although just as much stearine was 

 consumed at that altitude in a given time as at Chamouni, the 

 aspect of the flames was completely altered. They seemed, to 

 use their language, to be the mere ghosts of the flames "which 

 the same candles were competent to produce pale, feeble, and 

 suggesting a greatly diminished energy of combustion." 



The cause of the diminution of the light is not due to any 

 reduction of the rate of burning, but to a more perfect diffusive 

 effect ; the oxygen of the air penetrates the flame more perfectly, 

 and the matter of the flame passes more rapidly into the air ; 

 and thus, by the mutual interpenetration of the one into the 

 other, the carbon is more rapidly burnt out. Dr. Frankland also 

 discovered the interesting fact, that by compressing the air 

 round the flame of alcohol, which burns with a smokeless flame, 

 it became as bright as coal gas, and at a higher pressure could 

 even be made to smoke. The intensity of any given flame is 

 reduced 5 per cent, for every fall of one inch in the barometer, 

 or increased in the same proportion with each rise of one inch. 

 Dr. Frankland has also shown that the comparative cost of light 

 equal to that obtained from twenty sperm candles, each burning 

 ten hours at the rate of 120 grains per hour, would be as 

 follows : Wax, 7s. 2^d. ; spermaceti, 6s. 8d. ; tallow, 2s. 8d. ; 

 sperm oil, Is. lOd. ; coal gas, 4.|d. ; cannel gas, 3d. ; paraffin 

 candles, 3s. lOd. ; paraffin oil, 6d. ; rock oil, 7|d. Consequently 

 paraffin and rock oils are the best sources of light for domestic 

 purposes. They are the cheapest, give the greatest amount of 

 light, and, what is of still greater importance, they do this with 

 the least development of heat. 



The extraordinary light-giving agents, with the exception of 

 the combustion of magnesium in air or of phosphorus in oxygen, 

 require more elaborate apparatus than the beginner in science is 

 likely to be able to afford. The oxy-calcium light is one of the 

 most simple, and is obtained by forcing a jet of oxygen through 

 the flame of a spirit-lamp, and directing the resulting fire on to a 

 ball of lime. This light will do very nicely for the exhibition of 

 photographs on a small screen in a moderate-sized apartment. 



If a more brilliant light is required, the lime or oxy-hydrogen 

 light may be used. It is, of course, easy to place two volumes 

 of hydrogen and one of oxygen in a large bladder furnished 

 with a stop-cock, and then to burn the mixed gases from a Hem- 

 ming' s jet. This is undoubtedly the cheapest, but not the 

 safest method, especially if the bladder is squeezed by the hands. 

 A steady pressure is absolutely necessary, and this can only be 

 obtained by using pressure boards. Indeed, it is far better not 

 to attempt either the oxy-calcium or the oxy-hydrogen lights 

 without proper caoutchouc bags, pressure boards, and jets, all 

 of which may now be obtained at a very moderate price of the 

 instrument-makers. The cost of an accident to person or 

 property by the explosion of a large bladder full of the mixed 

 gases in a dwelling-room is very likely to be greater than the 

 purchase of the proper appliances. 



Although the electric light is the most brilliant artificial light 

 that can be procured, it is only thoroughly effective on a large 

 scale. A voltaic battery on Grove's principle, of forty cells 

 and a good electric lamp, will give excellent results, whilst a 

 smaller arrangement is continually flickering, and the constant 

 movement of the charcoal points becomes tiresome, and fatigues 

 the eyes of those who may be invited to see the experiments. 

 Here, again, a good apparatus is the cheapest in the, end. 



The magneto-electric machine will also give a continuous and 

 brilliant electric light, but as the armature must revolve many 

 hundred times in a minute, and can only be worked 1 effectively 

 with the aid of a steam-engine, such a light fa a luxury to be 

 used only by a rich, body such as the Trinity House brethren, 

 who have employed Professor Holmes' magneto*electric light 

 for many years- a-t the' North Foreland lighthouse.. 



The lighted 1 candle in the cottage window has* guided many a 

 weary husband 1 over- fell and moor to his; home;. but this magneto- 

 electric 3igM is so large in amount that, with proper optical: 

 arrangements; sucfe as Fresnel's lamp, it wiH flash its friendljy 

 rays tfpfiutj-five aailes across the ceean, and almost rival 



