H. Erdmann has made somewhat similar calculation, comparing the light of acetylene with that of the Hefner (amyl acetate) lamp, and with coal-gas consumed in an Argand and an incandescent burner. Consecutively taking the radiation of the acetylene flame as unity for each of the spectrum colours, his results are:
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| | | | |
| | | | Coal-Gas |
| Colour in | Wave-Lengths, | |_______________________|
| Spectrum | uu | Hefner Light | | |
| | | | Argand | Incandescent |
|___________|_______________|______________|________|______________|
| | | | | |
| Red | 650 | 1.45 | 1.34 | 1.03 |
| Orange | 610 | 1.22 | 1.13 | 1.00 |
| Yellow | 590 | 1.00 | 1.00 | 1.00 |
| Green | 550 | 0.87 | 0.93 | 0.86 |
| Blue | 490 | 0.72 | 1.27 | 0.92 |
| Violet | 470 | 0.77 | 1.35 | 1.73 |
|___________|_______________|______________|________|______________|
B. Heise has investigated the light of different flames, including acetylene, by a heterochromatic photometric method; but his results varied greatly according to the pressure at which the acetylene was supplied to the burner and the type of burner used. Petroleum affords light closely resembling in colour the Argand coal-gas flame; and electric glow-lamps, unless overrun and thereby quickly worn out, give very similar light, though with a somewhat greater preponderance of radiation in the red and yellow.
____________________________________________________________________
| | | |
| | Percent of Total | |
| Light. | Energy manifested | Observer. |
| | as Light. | |
|____________________________|___________________|___________________|
| | | |
| Candle, spermaceti . . | 2.1 | Thomsen |
| " paraffin . . . | 1.53 | Rogers |
| Moderator lamp . . . | 2.6 | Thomsen |
| Coal-gas . . . . . | 1.97 | Thomsen |
| " . . . . . | 2.40 | Langley |
| " batswing . . . | 1.28 | Rogers |
| " Argand . . . | 1.61 | Rogers |
| " incandesce . . | 2 to 7 | Stebbins |
| Electric glow-lamp . . | about 6 | Merritt |
| " " . . | 5.5 | Abney and Festing |
| Lime light (new) . . . | 14 | Orehore |
| " (old) . . . | 8.4 | Orehore |
| Electric arc . . . . | 10.4 | Tyndall; Nakano |
| " . . . . | 8 to 13 | Marks |
| Magnesium light . . . | 12.5 | Rogers |
| Acetylene . . . . | 10.5 | Stewart and Hoxie |
| " (No. 0 slit burner | 11.35 | Neuberg |
| " (No. 00000 . . | | |
| Bray fishtail) | 13.8 | Neuberg |
| " (No. 3 duplex) . | 14.7 | Neuberg |
| Geissler tube . . . | 32.0 | Staub |
|____________________________|___________________|___________________|
Violle and Féry, also Erdmann, have proposed the use of acetylene as a standard of light. As a standard burner Féry employed a piece of thermometer tube, cut off smoothly at the end and having a diameter of 0.5 millimetre, a variation in the diameter up to 10 per cent. being of no consequence. When the height of the flame ranged from 10 to 25 millimetres the burner passed from 2.02 to 4.28 litres per hour, and the illuminating power of the light remained sensibly proportional to the height of the jet, with maximum variations from the calculated value of ±0.008. It is clear that for such a purpose as this the acetylene must be prepared from very pure carbide and at the lowest possible temperature in the generator. Further investigations in this direction should be welcome, because it is now fairly easy to obtain a carbide of standard quality and to purify the gas until it is essentially pure acetylene from a chemical point of view.
L. W. Hartmann has studied the flame of a mixture of acetylene with hydrogen. He finds that the flame of the mixture is richer in light of short wave-lengths than that of pure acetylene, but that the colour of the light does not appear to vary with the proportion of hydrogen present.
Numerous investigators have studied the optical or radiant efficiency of artificial lights, i.e., the proportion of the total heat plus light energy emitted by the flame which is produced in the form of visible light. Some results are shown in the table on the previous page.
Figures showing the ratio of the visible light emitted by various illuminants to the amount of energy expended in producing the light and also the energy equivalent of each spherical Hefner unit evolved have been published by H. Lux, whose results follow:
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| | | | | |
| | Ratio of | Ratio of | Mean | Energy |
| | Light | Light | Spherical | Equiva- |
| Light. | emitted to | emitted to | Illuminat- | lent to 1 |
| | Total | Energy | ing Power. | Spherical |
| | Radiation. | Impressed. | Hefners. | Hefner in |
| | | | | Watts. |
|____________________|____________|____________|____________|___________|
| | | | | |
| | Per Cent. | Per Cent. | | |
| Hefner lamp | 0.89 | 0.103 | 0.825 | 0.108 |
| Paraffin lamp, 14" | 1.23 | 0.25 | 12.0 | 0.105 |
| ACETYLENE, 7.2 | | | | |
| litre burner | 6.36 | 0.65 | 6.04 | 0.103 |
| Coal-gas incandes- | | | | |
| cent, upturned | 2.26-2.92 | 0.46 | 89.6 | 0.037 |
| " incandes- | | | | |
| cent, inverted | 2.03-2.97 | 0.51 | 82.3 | 0.035 |
| Carbon filament | | | | |
| glow-lamp | 3.2-2.7 | 2.07 | 24.5 | 0.085 |
| Nernst lamp | 5.7 | 4.21-3.85 | 91.9 | 0.073 |
| Tantalum lamp | 8.5 | 4.87 | 26.7 | 0.080 |
| Osram lamp | 9.1 | 5.36 | 27.4 | 0.075 |
| Direct-current arc | 8.1 | 5.60 | 524 | 0.047 |
| " " enclosed | 2.0 | 1.16 | 295 | 0.021 |
| Flame arc, yellow | 15.7 | 13.20 | 1145 | 0.041 |
| " " white | 7.6 | 6.66 | 760 | 0.031 |
| Alternating- | | | | |
| current arc | 3.7 | 1.90 | 89 | 0.038 |
| Uviol mercury | | | | |
| vapour lamp | 5.8 | 2.24 | 344 | 0.015 |
| Quartz lamp | 17.6 | 6.00 | 2960 | 0.014 |
|____________________|____________|____________|____________|___________|
CHEMICAL PROPERTIES.--It is unnecessary for the purpose of this work to give an exhaustive account of the general chemical reactions of acetylene with other bodies, but a few of the more important must be referred to. Since the gases are liable to unite spontaneously when brought into contact, the reactions between, acetylene and chlorine require attention, first, because of the accidents that have occurred when using bleaching- powder (see Chapter V.) as a purifying material for the crude gas; secondly, because it has been proposed to manufacture one of the products of the combination, viz., acetylene tetrachloride, on a large scale, and to employ it as a detergent in place of carbon tetrachloride or carbon disulphide. Acetylene forms two addition products with chlorine, C_2H_2Cl_2, and C_2H_2Cl_4. These are known as acetylene dichloride and tetrachloride respectively, or more systematically as dichlorethylene and tetrachlorethane. One or both of the chlorides is apt to be produced when acetylene comes into contact with free chlorine, and the reaction sometimes proceeds with explosive violence. The earliest writers, such as E. Davy, Wöhler, and Berthelot, stated that an addition of chlorine to acetylene was invariably followed by an explosion, unless the mixture was protected from light; whilst later investigators thought the two gases could be safely mixed if they were both pure, or if air was absent. Owing to the conflicting nature of the statements made, Nieuwland determined in 1905 to study the problem afresh; and the annexed account is chiefly based on his experiments, which, however, still fail satisfactorily to elucidate all the phenomena observed. According to Nieuwland's results, the behaviour of mixtures of acetylene and chlorine appears capricious, for sometimes the gases unite quietly, although sometimes they explode. Acetylene and chlorine react quite quietly in the dark and at low temperatures; and neither a moderate increase in temperature, nor the admission of diffused daylight, nor the introduction of small volumes of air, is necessarily followed by an explosion. Doubtless the presence of either light, air, or warmth increases the probability of an explosive reaction, while it becomes more probable still in their joint presence; but in given conditions the reaction may suddenly change from a gentle formation of addition products to a violent formation of substitution products without any warning or manifest cause. When the gases merely unite quietly, tetrachlorethane, or acetylene tetrachloride, is produced thus: