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The volume changes of five gases under high pressures
98
CURRENT TOPICS.
[J. F. I.
The Volume Changes of Five Gases under High Pressures. P. VV-. BRIDGMAN. (Proc. Nat. Acad. Sci., Nov., I 9 2 3 . ) - - T h i r t y years ago Amagat examined the compressibilities of hydrogen and nitrogen under pressures extending to 3ooo kg. per square centimetre. In this paper the range for nitrogen, helium and argon is brought up to five times the former maximum pressure, while for hydrogen and ammonia it remains somewhat less. Under these enormous pressures Boyle's law is far from being followed. According to it, increasing the pressure from 3ooo to I5,ooo kg./cm. 2 should reduce the volume of nitrogen to one-fifth of what it was at the lower pressure. In fact, however, this change of pressure merely causes the volume of the gas at 68 ° C. to change from 36.I3 to 25.43. " The densities under I5,ooo kg. are as follows: Hydrogen, o.I3oI (extrapolated from 13,ooo); helium , 0.340 ; and nitrogen, I.IO2. These densities are greater than the densities of the liquid or solid phases of these substances under reduced temperatures at atmospheric pressure. Thus the density of liquid hydrogen is ordinarily given as o.o7o, and that of the solid as 0.076; the density of liquid helium is o.I456; and that of liquid nitrogen is in the neighborhood of 0.85. These figures enable lower limits to be placed on the compressibility of the liquid and solid phases, quantities for which previously we have had no idea of the order of magnitude. It appears that the compressibilities of solid and liquid hydrogen and of liquid helium are by far the greatest ever found for a solid or liquid, and it is probable that these are the most compressible liquids and solids." No equation of state seems to fit the experimental results, though an equation recently proposed by Becker predicts the changes in nitrogen quite well. G.F.S. A D e t e r m i n a t i o n of e/m from M e a s u r e m e n t s of the Z e e m a n Effect. H. D. BABCOCK. (Astrophys. Y., Oct., 1923.)--Webster and Page have given 1.7686 x IO7 as the most accurate value of the ratio of the electrical charge of an electron to its mass. Birge gives it as z.758 x ~o7 and suggests that a new determination be made from the Zeeman effect. When a line is converted into three lines by the application of a magnetic field, the ratio e/m is a function of the velocity of light in the medium where the wave-lengths are measured, the strength of the magnetic field, the wave-length of the original line and finally of the difference in wave-length between the original line and one of the outer lines of the triplet. From this e/m can be calculated. A field strength of about 30,0oo gausses was used. Chromium, zinc, barium and titanium lines were measured in the magnetic field. The weighted mean of the determination from 49 plates is e / m = 1.76I x Io 7, with a probable error of one part in I8OO. G . F . S .
CURRENT TOPICS.
[J. F. I.
The Volume Changes of Five Gases under High Pressures. P. VV-. BRIDGMAN. (Proc. Nat. Acad. Sci., Nov., I 9 2 3 . ) - - T h i r t y years ago Amagat examined the compressibilities of hydrogen and nitrogen under pressures extending to 3ooo kg. per square centimetre. In this paper the range for nitrogen, helium and argon is brought up to five times the former maximum pressure, while for hydrogen and ammonia it remains somewhat less. Under these enormous pressures Boyle's law is far from being followed. According to it, increasing the pressure from 3ooo to I5,ooo kg./cm. 2 should reduce the volume of nitrogen to one-fifth of what it was at the lower pressure. In fact, however, this change of pressure merely causes the volume of the gas at 68 ° C. to change from 36.I3 to 25.43. " The densities under I5,ooo kg. are as follows: Hydrogen, o.I3oI (extrapolated from 13,ooo); helium , 0.340 ; and nitrogen, I.IO2. These densities are greater than the densities of the liquid or solid phases of these substances under reduced temperatures at atmospheric pressure. Thus the density of liquid hydrogen is ordinarily given as o.o7o, and that of the solid as 0.076; the density of liquid helium is o.I456; and that of liquid nitrogen is in the neighborhood of 0.85. These figures enable lower limits to be placed on the compressibility of the liquid and solid phases, quantities for which previously we have had no idea of the order of magnitude. It appears that the compressibilities of solid and liquid hydrogen and of liquid helium are by far the greatest ever found for a solid or liquid, and it is probable that these are the most compressible liquids and solids." No equation of state seems to fit the experimental results, though an equation recently proposed by Becker predicts the changes in nitrogen quite well. G.F.S. A D e t e r m i n a t i o n of e/m from M e a s u r e m e n t s of the Z e e m a n Effect. H. D. BABCOCK. (Astrophys. Y., Oct., 1923.)--Webster and Page have given 1.7686 x IO7 as the most accurate value of the ratio of the electrical charge of an electron to its mass. Birge gives it as z.758 x ~o7 and suggests that a new determination be made from the Zeeman effect. When a line is converted into three lines by the application of a magnetic field, the ratio e/m is a function of the velocity of light in the medium where the wave-lengths are measured, the strength of the magnetic field, the wave-length of the original line and finally of the difference in wave-length between the original line and one of the outer lines of the triplet. From this e/m can be calculated. A field strength of about 30,0oo gausses was used. Chromium, zinc, barium and titanium lines were measured in the magnetic field. The weighted mean of the determination from 49 plates is e / m = 1.76I x Io 7, with a probable error of one part in I8OO. G . F . S .