90 



DNDULATORY FORCES. LIGHT. 



[COLOUR, ETC., OF FLAME. 



the case if very different ; for by intersecting the flame 

 with i cold plaU-, we shall find that there are myriads 

 rtf.U. of solid particles in the form of 



soot, which, by their ignition, pro- 

 duce that intensity of light for 

 which such combustibles are valued. 

 Again, when sulphur is burnt in 

 oxygen gas it evolves a faint blue 

 spectral light, that is hardly suffi- 

 i-u-nt to illuminate the dial of a 

 watch ; but when phosphorus is 

 treated in this manner, it omits a 

 volume of light that rivals in in- 

 tensity that of the sun. It will be 

 noticed tliat the products of the 

 former are wanting in solid par- 

 ticles, whereas those of the latter 

 are made up of myriads of white 

 flakes of solid phosphoric acid. It 

 is on this account that carbonic 

 oxide and wood-spirit, as well as 

 hydrogen, sulphur, and alcohol, 

 burn with little or 110 light ; while 

 zinc, antimony, ether, turpentine, 

 oil, tallow, and coal gas, burn with 

 more or less splendour. But we 

 may communicate a great degree of brilliancy to some 

 :if the former, by giving them a large proportion of 

 solid particles ; for example, when we sift a little mag- 

 nesia into a jet of hydrogen, its illuminating power 

 is at once raised to a high standard ; and the same 

 thing happens if we employ lime, oxide of zinc, or 

 white antimony, instead of the magnesia. So, also, if 

 we naphthalise the gas by passing it through a chamber 

 containing ether, turpentine, benzole, or coal naphtha, 

 its light is increased to that of the best descrip- 

 tion of coal gas. In fact, coal gas consists, in great 

 part, of hydrogen and carburetted hydrogen ; both of 

 which are, as it were, naphthalised with other compounds 

 that give it illuminating power. But the most striking 

 example that we can refer to in illustration of the fact 

 that the light of flame is dependent on the presence of 

 solid particles, is afforded by the results obtained with 

 the oxy-hydrogen blowpipe.* When the flame of the 

 mixed oxygen and hydrogen gases is seen as it issues 

 from the jet without impinging on any solid substance, 

 it strikes the observer as being an insignificant and 

 almost invisible object ; but directly it is thrown on a 

 piece of lime or other material that will give it solid 

 particles, it instantly becomes one of the most splendid 

 lights with which we are acquainted : in fact, the inten- 

 sity of the oxy-hydrogen light is so great, that when its 

 rays are reflected by means of a concave mirror, they are 

 distinctly visible at a distance of sixty-eight miles. We 

 can easily understand, therefore, why it was so earnestly 

 proposed by Lieutenant Druuunond, as a means of illu- 

 minating lighthouses. So, again, with the electric 

 light, the brilliancy of which is dependent on a number 

 of minute particles of charcoal that are intensely heated 

 by the galvanic current. The splendour of this light is 

 scarcely inferior to that of the sun ; for, on one occasion 

 when it was tested, it was found to be equal to that of 

 300,000 wax candles, and was distinctly seen at a dis- 

 tance of several miles. 



Lastly, it may be stated, as the converse of the pre- 

 ceding, that we can always reduce the illuminating power 

 of flame by diminishing the amount of solid material 

 contained in it. To take coal gas, by way of example, 

 we shall find that the light may be kept down, or even 

 destroyed altogether, by blowing atmospheric air into it. 

 This sometimes happens with the lights in the streets, 

 and then the flame is reduced to an insignificant blue 

 nicker. The same thing occurs if we mix atmospheric 

 air with the gas before it is consumed, or if we employ 

 a glass chimney that is too tall for the size of the flame. 

 In all these instances, the solid particles of charcoal r..n 

 tained in the gas are burnt too speedily, and, conse- 

 quently, there is no time for their previous ignition. 



Be* antr, p. 62. 



This teaches us that there is one great point always to be 

 attended to in the management of gas for illuminating 

 purposes : we should take care that the supply of atmo- 

 spheric air is so regulated that, on the one hand, the solid 

 particles shall not be instantly consumed ; and, on the 

 other, that they shall not escape as uncombined soot. 

 Many gas-burners are constructed so as to effect this of 

 themselves; this is the case with the fish-tail and the 

 bat's- wing, which present a thin stratum of flame for the 

 action of atmospheric oxygen. Other burners, as the 

 Argand and its modifications, require a glass or chimney 

 for the purpose of regulating a proper supply of air. 

 The chimney acts by creating a draught, and so causing 

 the air to play into the body of the flame ; but, if the 

 chimney be too high, the draught will be too great, and 

 the gas will be overburnt ; whereas, if it be too low, the 

 current of air will not be sufficiently strong, and the 

 carbon of the gas will escape in the form of soot or smoke. 

 As a rule, the flame should be kept at about one inch 

 below the top of the chimney. Mr. Billow, of London, 

 has contrived a burner, which not only demonstrates the 

 nature of flame, and the cause of its light, but also shows 

 the effects of an under supply of atmospheric air. In 

 ordinary burners the air is admitted to the flame on all 

 sides, and it even passes up into its interior ; but in the 

 burner contrived by Mr. Billow, the inner supply of 

 atmospheric air is cut off, and, consequently, the gas is 

 but imperfectly consumed. The result of this is that 

 carbon is liberated, and, by the construction of the 

 burner, it is made to gyrate round and round, until 

 it collects into little solid masses, which fall by reason of 

 their own weight : directly this happens they come into 

 contact with a part of the flame where combustion is 

 actively going on, and they are instantly projected into 

 the atmosphere like so many diminutive rockets, t 



Quantity and Intensity of Flame. It must have been 

 noticed again and again, by those who are in the habit of 

 pursuing their avocations by the aid of artificial light, 

 that there is a great difference in the practical value of 

 different kinds of illuminating agents : for example, the 

 eye is often most painfully excited with the strong glare 

 of certain varieties of light, although there is not enough 

 of it to produce the necessary illumination of surround- 

 ing objects ; on the other hand, we sometimes perceive 

 that the light is particularly inoffensive, notwithstanding 

 that everything about us is brightly and sufficiently 

 illuminated. It is probable that these two conditions 

 are entirely dependent on two states of light, which 

 have not yet been properly appreciated. To the one we 

 apply the term intensity, and to the other quantity. 

 We have examples of the former in the electric light, in 

 the Drummond light, and in the vivid combustion which 

 is going on in the burners of Leslie and Wingfield ; of 

 the latter in the diffused light of day, and in the illumi- 

 nation that is produced by a number of separated gas 

 jets. In the one case we have comparatively few solid 

 particles, but they are heated to a high degree of inten- 

 sity; in the other we have a much larger number of 

 ignited points, but their ignition is not carried to so 

 high a temperature. These facts have not yet received 

 so much attention as they deserve ; and in all our endea- 

 vours to improve the quality of a burner, we should 

 never lose sight of the fact, that the human eye requires 

 far more of quantity than it does of intensity for agree- 

 able vision. 



The Colour of Flame. Our preceding remarks have 

 gone to show that the light of flame is dependent 

 on the number of solid particles present in it : we will 

 now demonstrate that the colour of the light is de- 

 pendent on the nature of those particles. The flame of 

 alcohol or wood-spirit is naturally colourless; but we 

 may give it various tints by saturating the spirit with 

 different kinds of saline substances. Chloride of potas- 

 sium will make it violet; boracic acid or chloride of 

 barium, green ; chloride of copper, blue ; common 

 salt, yellow ; chloride of strontium, red ; and chloride 

 of lithium makes it of a carmine tint. The same 



< Our iradcru will find i dncription of thin burner t page 357 of th 

 ccond roluine of the Journal of 



