622
ARGON
required to form nitrous acid. The Argon ultimately found was 75‘0 c.c., or a little more than 1 per cent, of the atmospheric nitrogen used. A subsequent determination over mercury by Kellas (Proc. Roy. Soc. lix. p. 66, 1895) gave 1-186 c.c. as the amount of Argon present in 100 c.c. of mixed atmospheric nitrogen and Argon. In the earlier stages of the inquiry, when it was important to meet the doubts which had been expressed as to the presence of the new gas in the atmosphere, blank experiments were executed in which air was replaced by nitrogen from ammonium nitrite. The residual Argon, derived doubtless from the water used to manipulate the gases, was but a small fraction of what would have been obtained from a corresponding quantity of air. The other method by which nitrogen may be absorbed on a considerable scale is by the aid of magnesium. The metal in the form of thin turnings is charged into hard glass or iron tubes heated to a full red in a combustion furnace. Into this air, previously deprived of oxygen by red-hot copper and thoroughly dried, is led in a continuous stream. At this temperature the nitrogen combines with the magnesium, and thus the Argon is concentrated. A still more potent absorption is afforded by calcium, prepared in situ by heating a mixture of magnesium dust with thoroughly dehydrated quick-lime. The density of Argon, prepared and purified by magnesium, was found by Professor Ramsay to be 19-941 on the 0 = 16 scale. The volume actually weighed was 163 c.c. Subsequently large - scale operations with the same apparatus as had been used for the principal gases gave an almost identical result (19'940) for Argon prepared with oxygen. Argon is soluble in water at 12° C. to about 4"0 per cent., that is, it is about times more soluble than nitrogen. We should thus expect to find it in increased proportion in the dissolved gases of rain-water. Experiment has confirmed this anticipation. The weight of a mixture of Argon and nitrogen prepared from the dissolved gases showed an excess of 24 mg. over the weight of true nitrogen, the corresponding excess for the atmospheric mixture being only 11 mg. Argon is contained in the gases liberated by many thermal springs, but not in special quantity. The gas collected from the King’s Spring at Bath gave only one-half per cent., i.e,, half the atmospheric proportion. The most remarkable physical property of Argon relates to the constant known as the ratio of specific heats. When a gas is warmed one degree, the heat which must be supphed depends upon whether the operation is conducted at a constant volume or at a constant pressure, being greater in the latter case. The ratio of specific heats of the principal gases is 1"4, which, according to the kinetic theory, is an indication that an important fraction of the energy absorbed is devoted to rotation or vibration. If, as for Boscovitch points, the whole energy is translatory, the ratio of specific heats must be 1"67. This is precisely the number found from the velocity of sound in Argon as determined by Kundt’s method, and it leaves no room for any sensible energy of rotatory or vibrational motion. The same value had previously been found for mercury vapour by Kundt and Warburg, and had been regarded as confirmatory of the monatomic character attributed on chemical grounds to the mercury molecule. It may be added that helium has the same character as Argon in respect of specific heats (Ramsay, Proc. Roy. Soc. 1. p. 86, 1895). The refractivity of Argon is -961 of that of air. This low' refractivity is noteworthy as strongly antagonistic to the view at one time favoured by eminent chemists that Argon was a condensed form of nitrogen represented by N3. The viscosity of Argon is 1-21, referred to air, some-
what higher than for oxygen, which stands at the head of the list of the principal gases (“ On some Physical Properties of Argon and Helium,” Proc. Roy. Soc. vol. lix. p. 198, 1896). The spectrum shows remarkable peculiarities. According to circumstances, the colour of the light obtained from a Plucker vacuum tube changes “from red to a rich steel blue,” to use the words of Crookes, who first described the phenomenon. A third spectrum is distinguished by Eder and Yalenta. The red spectrum is obtained at moderately low' pressures (5 mm.) by the use of a Ruhmkorff coil without a jar or air-gap. The red lines at 7056 and 6965 (Crookes) are characteristic. The blue spectrum is best seen at a somew'hat lower pressure (1 mm. to 2-5 mm.), and usually requires a Leyden jar to be connected to the secondary terminals. In some conditions very small causes effect a transition from the one spectrum to the other. The course of electrical events attending the operation of a Ruhmkorff coil being extremely complicated, special interest attaches to some experiments conducted by Trowbridge and Richards, in which the source of power was a secondary battery of 5000 cells. At a pressure of 1 mm. the red glow of Argon was readily obtained with a voltage of 2000, but not with much less. After the discharge w'as once started, the difference of potentials at the terminals of the tube varied from 630 volts upwards. The introduction of a capacity between the terminals of the Geissler tube, for example two plates of metal 1600 sq. cm. in area separated by a glass plate 1 cm. thick,r made no difference in the red glow so long as the connexions w ere good and the condenser was quiet. As soon as a spark-gap was introduced, or the condenser began to emit the humming sound peculiar to it, the beautiful blue glow so characteristic of Argon immediately appeared. {Phil. Mag. xliii. p. 77, 1897.) The behaviour of Argon at low temperatures was investigated by Olszewski {Phil. Trans., 1895, p. 253). The following results are extracted from the table given by him:— Freezing Boiling Critical Critical Point, Point, Temperature, Pressure, Name. Cent. Cent. Atmos. Cent. -214-0 194-4 35-0 ■146-0 Nitrogen -189-6 187-0 50-6 121-0 Argon 1 •182-7 50-8 ■118-8 Oxygen The smallness of the interval between the boiling and freezing points is noteworthy. From the manner of its preparation it was clear at an early stage that Argon would not combine with magnesium or calcium at a red heat, nor under the influence of the electric discharge with oxygen, hydrogen, or nitrogen. Numerous other attempts to induce combination also failed. Nor does it appear that any well-defined compound of Argon has yet been prepared. It was found, however, by Berthelot that under the influence of the silent electric discharge, a mixture of benzole vapour and Argon underwent contraction, with formation of a gummy product from which the Argon could be recovered. The facts detailed in the original memoir led to the conclusion that Argon was an element or a mixture of elements, but the question between these alternatives was left open. The behaviour on liquefaction, however, seemed to prove that in the latter case either the proportion of the subordinate constituents was small, or else that the various constituents were but little contrasted. An attempt, somewhat later, by Ramsay and Collie to separate Argon by diffusion into two parts, which should have different densities or refractivities, led to no distinct effect. More recently Ramsay and Travers have obtained evidence of the existence in the atmosphere of three new gases,.
