134 



UNDULATORY FORCES. LIGHT. 



[THE OXY-HYDROGEN LUJUT. 



83 



8'3 

 6'4 

 6O 

 4O 

 3*0 

 2'6 

 2'3 

 each 



cubic foot of 



requires twenty-five candles' worth of light to give the 

 Mine amount of luminosity on the table ; and ao two or 

 throe g-.is-buruurs, consuming in all about ton cubic feet 

 of gat per hour, are fitted up to do the work of two 

 candles. It is this profusion of light and hoat which has 

 occasioned so strong a prejudice against the employment 

 of gas, on the score of its heating and vitiating effects ; 

 but the prejudice is not well-founded. Dr. Fraukland 

 has made experiments to determine the relative amounts 

 of carbonic acid produced by the usual illuminating 

 agents, and lie states that the following proportions of 

 carbonic avid are produced per hour during the com- 

 bustion of a sufficient quantity of each of the materials 

 to get the light of twenty sperm candles, each burning at 

 the rate of one hundred and twenty grains per hour : 



Tallow . . . . ' 10-1 cubic feet. 



Wax ..... 



Spermaceti ... 



Sperm oil . . . . 



Common London gas . . 



Manchester gas . . . 



London caunel gas . . 



Hydro-carbon Boghead gas 



Hydro-carbon Lesmahago gas" 

 Now, if we bear in mind that 

 carbonic acid involves the destruction of nearly five cubic 

 feet of air, and that, according to toxicologists, a pro- 

 portion of five per cent, of carbonic acid in the atmo- 

 sphere is dangerous to animal life, we shall perceive that 

 there is an enormous amount of atmospheric air vitiated 

 and rendered irrespirable from this cause alone ; but to 

 this must likewise be added an almost equally large 

 quantity of oxygen which is consumed by the hydrogen 

 of these illuminating agents, and which in coal gas 

 amounts in many cases to nearly fifty per cent. It will 

 be manifest, therefore, that in obtaining artificial light 

 by any of these means, we destroy a large quantity of 

 atmospheric air ; and hence provision should be made 

 for an ample supply of it by means of good ventilation. 

 This will be still more evident from wliat follows. 



Mr. Lewis Thompson has instituted a set of experi- 

 ments for the purpose of ascertaining how long a name 

 of a given intensity, obtained from different illuminating 

 agents, will burn in a given bulk of atmospheric air. In 

 all cases the value of the light emitted was the same 

 namely, that of tliirteen standard sperm candles, each of 

 one hundred and twenty grains' consumption per hour ; 

 and a distinct experiment was made with each agent. 

 The times that elapsed before the flames were extin- 

 guished were as follows : 



Rape or Colza oil . . . 71 minutes. 



Olive oil .... 72 



Russian tallow "... 75 



Town tallow .... 76 



Sperm oil .... 76 



Stearic acid .... 77 



Wax candles .... 79 



Spermaceti candles ... 83 



Common coal gas ... 98 



Canuel coal gas . . . 152 

 These times are inversely as the salubrity of the illumi- 

 nating agent ; and hence it follows that common rape oil 

 is the mo.it destructive of the atmosphere, and rich 

 cannel gas the least. 



The same is true of the heating effects of these bodies. 

 Already we have alluded to this fact ; but as it lias been 

 made the subject of special experiment by Mr. Lewis 

 Thompson, we will a^aiu refer to it. lie says, that when 

 the following materials are burnt for an hour, in such 

 quantity as to give the light of one sperm candle of one 

 hundred and twenty grains' consumption, they raised 

 the following amounts of water from the temperature of 

 60" to 212 Fall. : 



Cannel gas rained 4074 grains of water 152 



Common gas 



Sperm caudle 



Tallow candle 



Colza oil 7870 



" The impossibility of maintaining one uniform rate of 



G840 

 7:><5 



consumption in the case of the candle and oil, detract* 

 slightly from tiie value of the results ; but the indica- 

 tions are too decisive to permit the general conclusion 

 to be doubted that, light for light, the inconvenience 

 arising from heat is much less with gas than with any of 

 the ordinary agents employed to give light ; and in the 

 case of caunel gas the advantage is very great." 



ILLUMINATING AGENTS WHICH DO NOT 

 VITIATE THK ATMoSl'HEUE. 



OF these there are two which are especially deserving 

 of notice : they are the oxy-hydrogcu, or Druuimonu 

 light, and the electric light. 



The Ojcy-hydroyen Light. This was first introduced to 

 public notice by Lieutenant Drummoud. It consists of 

 a jet of oxygen and hydrogen gases, or of alcohol and 

 oxygen, burning so as to ignite a piece of lime or mag- 

 nesia ; and the high temperature which is thus produced, 

 renders the earthy body so incandescent as to be in- 

 tensely luminous. 



The apparatus wliich is employed for the production 

 of this light has, at various times, undergone consider- 

 able alteration and improvement. Originally the mixed 

 gases, consisting of two parts, by measure, of hydrogen 

 and one of oxygen, were condensed, by means of a 

 syringe worked at great pressure, into a square metal 

 box, from wliich there issued a long jot, of very small 

 bore ; this jet passed through a thick oak partition, in 

 order tlia't the operators might be protected from the 

 danger wliich was incidental to the bursting of the 

 metal box from explosion. This was the form of appa- 

 ratus originally contrived by Clarke and Newman. 

 After this the safety-jets of Guruey, Hemming, and 

 others, were adopted ; and at the present time, it is 

 customary to burn the mixed gases by means of the 

 hitter, or else to deliver the gases separately into a 

 double jet or nozzle, where they mix immediately before 

 they are consumed. Both of these plans are very 

 manageable, though the latter is thought to be loss 

 open to the risk of explosion than the former. 



The hydrogen gas is obtained by acting on zinc with 

 dilute sulphuric acid (one of acid to ten or twelve of 

 water) ; and the oxygen, by heating a pulverulent mixture 

 of four parts of chlorate of potash and one of peroxide 

 of manganese in a glass retort. In each case the gas is 

 to be collected in a gasometer, or else in bladders fixed 

 to receivers over a pneumatic trough. Mr. Watson has 

 obtained a patent for procuring the gases already mixed 

 in proper portions by the decomposition of water by 

 galvanic agency; but the process is an expensive one. 



When the mixed gases are burnt, the flame is projected 

 upon a small cylinder of lime or magnesia, which is from 

 time to time turned round, so as to expose a fresh sur- 

 face to the action of the flame. 



Another mode of obtaining this light is to throw a jet 

 of oxygen into a flame of spirit of wine or ether, or to 

 mix the oxygen with coal gas instead of with hydrogen. 



The light which is obtained by either of these plans is 

 very intense. When concentrated by means of a con- 

 cave mirror, it is distinctly visible at a distance of sixty- 

 five miles ; and when compared with the light of a wax 

 caudle, the mixture of oxygen and coal gas is equal to 

 twenty-nine of such candles ; that of alcoliol and oxygen 

 to sixty-nine ; that of ether and oxygen to seventy-six ; 

 and that of hydrogen and oxygen to a hundred and fifty- | 

 three. In consequence of the great intensity of the [ 

 oxy-hydrogen light, it is generally employed for the | 

 phantasmagoria, the dissolving views, and solar micro 

 scope, and for theatrical illuminations, and experiment. ; 

 in optics ; besides which, it has been recommended for j 

 lighthouses and signal-lights. The light differs from all 

 others which have been described, in the circumstance of 

 its being exceedingly white, and therefore well suited for 

 the display of bright and delicate colours. With this light 

 the various shades and tints of a picture or dress are as 

 plainly diaoarnibla as they are by the diffused light of day. 



The Electric Liqht. Within the last few years, public 

 expectation has been raised to a great height, by the 



