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Emulsions showing chromatic effects
862
CURRENT TOPICS.
[J. F. I.
and on mountains. In addition samples of air have been brought down for examination and the radioactivity of wires carried b y kites and balloons has been studied. In this p a p e r the measurements were carried out b y means of airplanes flying horizontally. T h u s the m e a n value for the horizontal layer was effective in producing the readings and the speed of the plane produced a uniform flow of air through the a p p a r a t u s . After examination the method of absorbing the e m a n a t i o n in charcoal was rejected in favor of a condensation method. T h e forward motion of the airplane drove air into a mouthpiece from which it was led into a little cooling tower where it was freed from w a t e r v a p o r and C02 t h a t m i g h t clog the a p p a r a t u s . Thence it proceeded to a plate condenser, cooled b y liquid air, where the e m a n a t i o n was deposited. A b o u t 8 kg. of liquid air had to be t a k e n along in a flight. W h e n the desired height had been attained the pilot was directed to proceed at the same level and air was a d m i t t e d to the condenser for not more t h a n 7 minutes. After landing the e m a n a t i o n was removed and its a m o u n t measured. In a single flight three different experiments could be made. T h e flights were m a d e near Berlin. Five successful ascensions were m a d e on three of which determinations were made at three elevations. T h e results show" clearly a decrease of radium e m a n a t i o n with elevation. For example in one flight at a height of from 55o to 6oo m. the e m a n a t i o n , expressed in lO -18 curies per cu. cm., was I68; a t 2,200-2,400 m. it was 24, while for 3,800 m. no e m a n a tion was found. In no case was a n y e m a n a t i o n detected at 2,4oo m. or over. Of course the derivation and previous history of the mass of air through which the horizontal flight is made have much influence on the e m a n a t i o n content. T h e authors claim t h a t their results prove the r a d i u m e m a n a t i o n in the air to be derived from the earth, at least on the days of the flights, M e a s u r e m e n t s of e m a n a t i o n content were made also in the physical l a b o r a t o r y of the University of Halle where in one room it reached I3,8oo of the units n a m e d above. This high value m a y have been due to the long use of radium in the laboratory. On top of the tower values were obtained six times as large as in the adjacent garden. This was a t t r i b u t e d to the smoke of the city in which e m a n a t i o n m a y have condensed. G. F. S. The thirteenth n u m b e r of the Annalen der Physik for 1928 is interesting from the fact t h a t of its five articles three are b y women. T h e two shorter papers b y men come first and are followed b y
June. 1929.]
CURRENT T o m c s .
863
"Experimental Investigations on W. Ritz's Theory of the Transversal Vibrations of Quadrilateral Plates" by Alice Lemke. This is succeeded by Frida Stadie's discussion of "Problems of Brownian Movements." The final contribution is " O n the Magnetic Properties of Cobalt" by Margarete Samuel. In this last paper two rods of cobalt were investigated. T hey came from different sources, Krupp's Works at Essen and the Kaiser Wilhelm Institute for the Investigation of Iron in Dfisseldorf. They contained 1.33 and 1.5 per cent. iron respectively. Unfortunately it was impossible to get cobalt free from iron for the experiments. An attempt made at the Institute to prepare a rod of cobalt from Kahlbaum's powdered metal free from both iron and nickel failed because the resulting rod became porous upon cooling. The outstanding feature of the results is that the two rods differed greatly in their magnetic properties and no thermal treatment was found that could make them agree. G. F. S.
Emulsions Showing Chromatic Effects. R. H. HUMPHREY. Glycerol has a refractive index of 1.467 that lies between the index of benzene 0.502) and that of acetone (I.359). " A stable emulsion of glycerol in acetone may be made by using pyroxylin (I to 2 per cent.) as the emulsifying agent; such emulsions are milky, the glycerol being the disperse phase." The index of the dispersion medium may be increased continuously by adding benzene which mixes with the acetone. When its index becomes the same as that of the glycerol the emulsion becomes clear. The equality of the indices holds however only for a particular wave-length and when the emulsion is viewed in white light it is this wave-length that gets through. The light transmitted in this case has the color of this one wave-length. The other wave-lengths present in white light are refracted and reflected many times so that the scattered light is of the color complementary to the transmitted light. By the addition of benzene to the emulsion the transmitted color changes from violet through green to orange, with corresponding changes in the scattered light. The addition of acetone makes the transmitted colors return in the reverse order to violet. "A change of I ° C. causes a perceptible change of the colour, the change being, for a fall of temperature, in the same direction as for increasing proportion of benzene." G. F. S.
(Proc. Phys. Soc., London, Vol. 4 I, Pt. I.)
CURRENT TOPICS.
[J. F. I.
and on mountains. In addition samples of air have been brought down for examination and the radioactivity of wires carried b y kites and balloons has been studied. In this p a p e r the measurements were carried out b y means of airplanes flying horizontally. T h u s the m e a n value for the horizontal layer was effective in producing the readings and the speed of the plane produced a uniform flow of air through the a p p a r a t u s . After examination the method of absorbing the e m a n a t i o n in charcoal was rejected in favor of a condensation method. T h e forward motion of the airplane drove air into a mouthpiece from which it was led into a little cooling tower where it was freed from w a t e r v a p o r and C02 t h a t m i g h t clog the a p p a r a t u s . Thence it proceeded to a plate condenser, cooled b y liquid air, where the e m a n a t i o n was deposited. A b o u t 8 kg. of liquid air had to be t a k e n along in a flight. W h e n the desired height had been attained the pilot was directed to proceed at the same level and air was a d m i t t e d to the condenser for not more t h a n 7 minutes. After landing the e m a n a t i o n was removed and its a m o u n t measured. In a single flight three different experiments could be made. T h e flights were m a d e near Berlin. Five successful ascensions were m a d e on three of which determinations were made at three elevations. T h e results show" clearly a decrease of radium e m a n a t i o n with elevation. For example in one flight at a height of from 55o to 6oo m. the e m a n a t i o n , expressed in lO -18 curies per cu. cm., was I68; a t 2,200-2,400 m. it was 24, while for 3,800 m. no e m a n a tion was found. In no case was a n y e m a n a t i o n detected at 2,4oo m. or over. Of course the derivation and previous history of the mass of air through which the horizontal flight is made have much influence on the e m a n a t i o n content. T h e authors claim t h a t their results prove the r a d i u m e m a n a t i o n in the air to be derived from the earth, at least on the days of the flights, M e a s u r e m e n t s of e m a n a t i o n content were made also in the physical l a b o r a t o r y of the University of Halle where in one room it reached I3,8oo of the units n a m e d above. This high value m a y have been due to the long use of radium in the laboratory. On top of the tower values were obtained six times as large as in the adjacent garden. This was a t t r i b u t e d to the smoke of the city in which e m a n a t i o n m a y have condensed. G. F. S. The thirteenth n u m b e r of the Annalen der Physik for 1928 is interesting from the fact t h a t of its five articles three are b y women. T h e two shorter papers b y men come first and are followed b y
June. 1929.]
CURRENT T o m c s .
863
"Experimental Investigations on W. Ritz's Theory of the Transversal Vibrations of Quadrilateral Plates" by Alice Lemke. This is succeeded by Frida Stadie's discussion of "Problems of Brownian Movements." The final contribution is " O n the Magnetic Properties of Cobalt" by Margarete Samuel. In this last paper two rods of cobalt were investigated. T hey came from different sources, Krupp's Works at Essen and the Kaiser Wilhelm Institute for the Investigation of Iron in Dfisseldorf. They contained 1.33 and 1.5 per cent. iron respectively. Unfortunately it was impossible to get cobalt free from iron for the experiments. An attempt made at the Institute to prepare a rod of cobalt from Kahlbaum's powdered metal free from both iron and nickel failed because the resulting rod became porous upon cooling. The outstanding feature of the results is that the two rods differed greatly in their magnetic properties and no thermal treatment was found that could make them agree. G. F. S.
Emulsions Showing Chromatic Effects. R. H. HUMPHREY. Glycerol has a refractive index of 1.467 that lies between the index of benzene 0.502) and that of acetone (I.359). " A stable emulsion of glycerol in acetone may be made by using pyroxylin (I to 2 per cent.) as the emulsifying agent; such emulsions are milky, the glycerol being the disperse phase." The index of the dispersion medium may be increased continuously by adding benzene which mixes with the acetone. When its index becomes the same as that of the glycerol the emulsion becomes clear. The equality of the indices holds however only for a particular wave-length and when the emulsion is viewed in white light it is this wave-length that gets through. The light transmitted in this case has the color of this one wave-length. The other wave-lengths present in white light are refracted and reflected many times so that the scattered light is of the color complementary to the transmitted light. By the addition of benzene to the emulsion the transmitted color changes from violet through green to orange, with corresponding changes in the scattered light. The addition of acetone makes the transmitted colors return in the reverse order to violet. "A change of I ° C. causes a perceptible change of the colour, the change being, for a fall of temperature, in the same direction as for increasing proportion of benzene." G. F. S.
(Proc. Phys. Soc., London, Vol. 4 I, Pt. I.)