Chemistry and Physics. 413 
oun NTE EOC ENE LIGEN OF. 
I. CHEMISTRY AND PuHysIcs. 
1. The refractivity and viscosity of Argon and Helium.—At 
the recent meeting of the British Association, Lorp RayiricH 
read a paper on the refractivity and viscosity of these gases. He 
described how, by means of an electric arc, kept up for several 
weeks in a mixture of oxygen and atmospheric nitrogen, he finally 
obtained more than a litre of argon at atmospheric pressure. This 
proved to have the same density as the specimen obtained by the 
magnesium method. The refractive index was measured by the 
interference method of Fizeau, the two beams being separated by 
slits in front of the lens nearest the eyepiece. The latter was 
constructed of cylindrical lenses. T’o avoid the use of cross-wires, 
the tubes containing the gases under comparison were arranged 
so as not. to occupy the whole field of view, some light passing 
parallel to and outside them; two sets of fringes were thus 
obtained, which could be brought to coincidence by varying the 
pressure of either gas. Adjustments were made for several pres- 
sures, one of the tubes always containing air. The values of the 
refractivity (~—1) were, for argon 0°961, and for helium 0°146, 
that of air being taken as unity. The viscosity of each gas was 
measured by its rate of flow through a capillary tube, the results 
being (air=1) argon 1:21, helium 0°96. Lord Rayleigh men- 
tioned that a sample of nitrogen collected from a Bath spring, 
where it bubbles out along with the water, gave the D, line of 
helium. Dr. Gladstone showed that the results of these experi- 
ments assign to argon the atomic weight 20, its specific refrac- 
tive energy being intermediate between those of fluorine and 
sodium, but not between those of potassium and calcium.—Nature, 
lii, 533. 
2. On the compound nature of the gas from Cleveite.—In the 
paper on the constituents of the gas from cleveite, alluded to in 
the last number, C. RunceE and F. PascuEn show that it must be 
regarded as made up of two and only two constituents. One of 
these, to which the bright yellow double line belongs, it is proposed 
to call helium,—this has the stronger spectrum; the other con- 
stituent as yet remains unnamed. After stating this conclusion 
and the theoretical grounds upon which it is based, the authors 
go on to say: | 
We have confirmed this rather hypothetical conclusion by the 
following experiment. The connection leading from our supply 
of cleveite gas to the vacuum tube contained a side branch part- 
ing from it and joining it again. There were stopcocks on either 
side of the side branch, and a third one in the side branch. In 
the main tube between the ends of the side branch a plug of 
asbestos was tightly inserted. To prepare the vacuum tube only 
the tap leading to the supply was closed, the whole space up to 
