TABLE I.

In addition, having measured the temperature coefficient of the decomposition of chlorophyll applied to photographic paper and, after exposure, having washed the chlorophyll off the paper with alcohol and subjected the brown solution obtained to electrophotometry, the author found by this method a temperature coefficient of 1.285. The indicated method of washing off the chlorophyll gives a somewhat diminished figure. More exact results could be obtained by electrophotometry of the paper in reflected light. On the basis of the figures obtained, the author concludes that the medium of the solvent has a considerable influence on the temperature coefficient of the photochemical decomposition of chlorophyll.

C. Wagner.

A Continuous Ultraviolet Spectrum.

G. Gehlhoff. Ueber eine konstante Lichtquelle mit kontinuierlichem ultravioletten Spektrum. ZS. für techn. Phys. 10, p. 224, (1921).

Usually a continuous ultraviolet spectrum is obtained either with the aid of an arc or by means of the Angerer spark (Al electrodes in water). If the first method is unsuitable because of its inconstancy, then the second is difficult enough to set up. The author therefore proposes, as a constant source of continuous ultraviolet spectrum, a half-watt incandescent lamp with a metallic filament. He investigated two lamps in parallel: one with a tantalum filament and a second with a tungsten spiral.

The distribution of energy in the spectrum was calculated by him according to Aschkinass’s formula for metals.

The ratio of the energy in the ultraviolet part of the spectrum from 0.3 μ to 0.4 μ to the energy of the visible spectrum (0.4 μ—0.8 μ) is 0.22%, and, under overload at 30%, 1.23% for the tantalum lamp; the corresponding values for the tungsten lamp are 1.17% and 2.02%. When photographic plates are used, these ratios become still more favorable. In the same ratio, the energy in the spectral region 0.3 μ—0.4 μ to the energy in the region 0.4 μ—0.5 μ is expressed by the following values:

For the tantalum lamp: 7.2%, under overload at 30% — 17.7%.

For the tungsten lamp: 16.9%, under overload at 30% — 21.6%.

The author’s lamps are a sphere 10 cm in diameter, filled with nitrogen or argon. A tube is attached to the sphere, to which a quartz plate or lens is fastened by sealing wax. For ordinary absorption measurements, a tantalum strip 25 mm long and 2–3 mm wide is sufficient, at a voltage of 6–8 volts and a load of up to 20 amperes. At the same voltage (6–8 V) and the same load (15–20 amp.), a tungsten spiral is sufficient with a length of 10 mm and a wire thickness of 0.5 mm. The advantages of such a source of ultraviolet light are self-evident.

T. Molodyi.