204 AXXUAL OF SCIENTIFIC DISCOVERT. 



were ro-Tink'd as alike obscure and useless. Aluminum is remarkable for its 



n 



lightness, being only about one-fourth the weight of silver; but magnesium 

 weighs only about two-thirds as much as aluminum, its specific gravity 

 bung only 1.74. It is of a silvery whiteness, undergoes no change in dry 

 air, and is subject to but slow oxidation in a damp atmosphere, and that 

 only quite superficially; it may be hammered, filed, and drawn into threads. 

 It is prepared by decomposing the chloride of the metal at a red heat, in a 

 close crucible, by means of potassium or sodium. The metal takes fire at 

 the temperature at which bottle-glass melts, and burns with a quiet and 

 excessively vivid light. 



The intensity of the light thus produced, as determined by Bunsen, is only 

 525 times less than that of the sun. Compared with an ordinary candle, it 

 appeared that a wire of magnesium 0.297 millimetre [1 mm. = 0.0394 inch] 

 in diameter produced as much light in burning as seventy-four stearine 

 candles, five to the pound. In order to support this light during one minute 

 a piece of wire 0.087 metres long, weighing 0.1204 gram [1 gram = 15.4325 

 grains], was required. 



Only 72.2 grams of magnesium, therefore, would be needed, in order to 

 maintain during ten hours an amount of light equal to that of seventy-four 

 stearine candles, consuming about 10.000 grams of stearine. 



According to Bunsen, magnesium wire is readily obtained by forcibly 

 pressing the metal through a hot steel die by means of a steel piston. Bun- 

 sen's arrangement for burning the wire was made by connecting spools of 

 it with rollei-s moved by clock-work, so that the wire should be unrolled like 

 the ribbon of paper in Morse's tele-graph. The end of the wire, thus gradually 

 pushed forward, passed into the flame of an ordinary alcohol lamp, where it 

 took fire. 



It is evident that a magnesium lamp of this sort must be much simpler 

 and more compendious than any of the existing arrangements of the electri- 

 cal or of Drummond's light; for light-houses, etc., where an intensely 

 brilliant illumination is required, it can hardly fail to rival either of these. 

 "Where an extraordinary amount of light is needed, it could readily be pi - o- 

 duccd by burning large wires, or several thin ones at the same time. Another 

 important consideration is the fact that the spools of wire, as well as the 

 clock-work and spirit-lamp, arc easily transportable. 



It is not, however, to the intensity alone of the magnesium flame that these 

 lamps owe their utility, for the photo-chemical (/. e., photographical) effect 

 of the IL.lit is also very great; according to Bunsen, the photo-chemical 

 power of the sun being only 3G.6 times greater than that of the magnesium 

 flame. The latter must therefore be useful in photographing by night, or in 

 any dark or subterranean locality ; the evenness and remarkable tranquil- 

 lity of the flame especially commending it for this purpose. 



The present high price of magnesium, it is true, must prevent any ex- 

 tended use of it for technical purposes. For example, Lenoir, of Vienna, 

 charges 3 florins [1 Fl. = 51 cents] for a gram of it; hence the cost per 

 minute of the light just described would be 36 Neukrculzer [1 ktr. = about 

 five-sixths of a cent], and the cost during ten hours would amount to 216 

 florins, while the ten kilogrammes of stearine could be procured for less 

 than 14 florins. But, even at this price, it could still be used by photog- 

 raphers, since it would only be required for exceedingly short intervals of 

 time, and all unnecessaiy consumption of the wire might be prevented by 

 stopping the clock-work. 



