190 



NATURE 



[Decembi r 23, 1897 



Mean 



I 5967 

 0-449S 



helium were compared. Taking the refractivity of the mixture 

 as unity, the following ratios were found : — 



Hydrogen/mixture ... i'S977 



1-5957 



Helium/mixture ... 04513 



0-4478 



The calculated values are — 



(•044 95 ^ 20 -1 2) _ 22-21 



4072 

 (1-5967 X 20 -60) _ 80-8 7 



4072 102-99 



Here the calculated value of the refractivity of the mixture is 

 3 per cent, higher than the found value, while with air the 

 calculated value is 0-35 per cent, too low. 



A third experiment was made, in which the "artificial air" 

 was a mixture of 19-13 cc. of carbon dioxide with 19-29 c.c. of 

 oxygen, both gases supposed to be at 0° and 760 mm. Again, 

 taking the refractivity of the mixture as unity we found the 

 following ratios : — 



Carbon dioxide/mixture ... 1-2450 



Oxygen/mixture 07525 



The calculated values are : — 



(^•^450 X 1913) = 61-99. 

 3842 



(0752 5 X 1 9 -29) _ 3778 

 38 42 ^ 99 -77 



Here, as with air, the total refractivity found is less than that 

 calculated. It is true the difference is not great, but we are 

 persuaded that it is real, for it considerably exceeds the error of 

 our several determinations. 



The case is not bettered if Lorentz and Lorenz's formula be 

 substituted for Gladstone and Dale's. Using their formula, 

 n^ - i/u' + 2, the calculated result is 99 72 per cent, of that 

 found for air. 



The coefficient of compressibility of hydrogen is too small, 

 while that of other gases, such as oxygen and nitrogen, is too 

 great. The effect of mixing equal volumes of hydrogen and 

 helium, each of which has too large a coefficient of elasticity, is 

 to cause each to occupy twice the volume that they previously 

 occupied, and to halve approximately the pressure for each. 

 The pressure is, therefore, lower than it would be for an abso- 

 lutely ideal gas, for each gas, hydrogen and helium. The sum 

 of these pressures will accordingly be too low, or transposing, 

 the sum of the volumes will be too great. The opposite argu- 

 ment holds for air. 



Now, in considering volumes, we deal not merely with the 

 CO- volume, i.e. the space occupied by the molecules,, but also 

 with the interstitial space inhabited by the molecules. But the 

 refractive power, if Clausius's deduction from the formula 

 of Lorenz and Lorentz is correct, is a function of the 

 dielectric constant, and hence of the co-volumes of the 

 gases. And here the discrepancy is more easily detected 

 than by any determination of density. It must, therefore, be 

 concluded that gases are not, as postulated by Dalton, in- 

 different to one another's presence, but that they modify one 

 another's properties in the same manner as do liquids, though to 

 a different extent. This mutual action at high pressuires and 

 small volumes modifies even the volume relations, as recently 

 shown by Dr. Kuenen. And it must persist at low pressures 

 and large volumes, though it may not always be possible to make 

 measurements of pressure and volume accurate enough to lead 

 to its detection; The refractivity, however, seems to be a 

 means delicate enough to be used for this purpose. 



"The Electric Conductivity of Nitric Acid." By V. H. 

 Veley, F. R.S., and J. J. Manley, Daubeny Curator of the 

 Magdalen College Laboratory, Oxford. 



In this paper an account is given of determinations of the 

 electric conductivity of nitric acid of percentage strengths from 

 1-3 to 99-97, purified from nitrous acid, sulphuric acid and the 

 halogen acids. Special forms of apparatus, and special methods 

 of measurements were adopted to overcome the difficulties of 

 polarisation of the concentrated acid. 



The chemical and certain physical properties of the practically 

 anhydrous acid were studied ; this acid has no action on various 

 metals such as copper, silver, cadmium, mercury, magnesium, 



NO. T469, VOL. 57] 



in ii and tin, nor on calcium carbonate either at ordinary tem- 

 peratures or at the boiling point. Sulphur and iron pyrites 

 dissolve quickly and completely in the gently-warmed acid. The 

 values are given for the corrected density at 4/4, 14-2/4 and 

 24-2/4 of the 99-97 acid, as also for thirty-two samples of acid 

 of Ko X 10*, K]^5 X 10*, KgQ X lo*, viz. conductivity in mercury 

 units, and for aio*, and ^Sio", the temperature coefficients in the 

 equation R/ = R,, (i -oU-^^fi). It is shown that whereas nitric 

 acid behaves as other electrolytes in possessing a positive 

 temperature coefficient of conductivity for percentage strengths 

 from I '3 to 96-12, yet from this point upwards it behaves as a 

 metallic conductor. The results of the experiments point to the 

 existence of hydrates of nitric acid containing loH.^O, 3H2O, 

 2H._,0 and HoO, with one molecular proportion of HNO3 and of 

 iHgO with 2HNO3, or H4N2O;, the analogue of pyrophosphoric 

 acid. Evidence is thus added to that previously accumulated of 

 definite combinations of nitric acid with water. 



Chemical Society, December 2. — Prof. Dewar, President, 

 in the chair. — The following papers were read : — The representa- 

 tion of the isomeric benzene hexachlorides by Collie's space- 

 formula, by F. E. Matthews. The author shows that Collie's 

 space-formula for benzene satisfactorily explains the existence of 

 two benzene hexachlorides ; amongst other facts explained are 

 the different stability of the isomerides and the formation of only 

 two. — Compounds of piperidine with phenols, by O. Rosenheim 

 and P. Schidrowitz. A number of addition products of piperi- 

 dine and phenols or their derivatives of a salt-like nature have 

 been prepared in which the phenol acts as an acid ; they are 

 crystalline, and are decomposed by str6ng alkalis or acids. 



Royal Meteorological Society, December 15. — Mr. E. 

 Mawley, President, in the chair. — Mr. W. Marriott read a paper 

 on the rainfall of Seathwaite, Cumberland. This place has long 

 been noted for its heavy rainfall, being in fact one of the wettest 

 spots in the British Isles — the average yearly amount is 137 

 inches. The spring months of April, May and June are the 

 driest, so they not only have the least rainfall, but also the least 

 number of rainy days. Augu.st, the month when the Lake 

 District is thronged with visitors, has the greatest number of 

 rainy days. The heavy nature of the rainfall may be gathered 

 from the fact that 21 per cent, of the falls are above i inch, 2 per 

 cent, being above 3 inches. The greatest fall in one day was 

 8-03 inches on November 12. The author has investigated the 

 atmospheric conditions under which the heavy rainfalls occurred 

 at Seathwaite, and he finds that these heavy falls are due to the 

 direction and force of the wind. When the wind is blowing 

 strongly from the south-east or south-west, it will be concen- 

 trated in the valleys on the windward of Scafell, and rush up 

 them with considerable force, the air current consequently being 

 projected to a considerable altitude beyond Scafell. Owing to 

 the reduction of temperature with elevation, the air parts with a 

 great deal of its moisture, which falls as rain. With such a 

 process going on continuously for a whole day, the heavy rain- 

 fall at Seathwaite is fully accounted for. — Mr. R. C. Mossman 

 also read a paper on the daily values of non-instrumental 

 meteorological phenomena in London from 1763 to 1896. The 

 phenomena discussed were thunderstorms, lightning without 

 thunder, fog, snow, hail and gales. 



Cambridge. 



Philosophical Society, December 6. — Mr. F. Darwin, 

 President, in the chair. — Features of interest in the fauna 

 of the Sandwich I.slands (with exhibitions), by Mr. R. C. L. 

 Perkins. Mr. Perkins exhibited and read>some notes on some 

 of the more interesting insects from the Hawaiian Islands. 

 Several species of endemic dragon-flies {Agriotiince) were 

 shown, some of which passed their earlier stages in water, 

 in the usual manner, while others in the nymph state lived 

 amongst the leaves of a liliaceous plant, the diversity in habit 

 having probably been brought about by the extreme poverty of ' ■ 

 the freshwater fauna, the terrestrial species being much more ' | 

 favourably situated in regard to a constant supply of food. A 

 series of examples of thi-ee or four allied species of Longicorn 

 beetles of the genus Plagithmystts were remarkable for their 

 extreme variability in colour, in spite of their limited range. 

 The varieties of each species fell into two or three groups, which _ 

 were hardly, if at all, connected by intermediate forms. The r.l 

 differences between the extreme forms of a species were in some ' '^ 

 cases more striking than the differences between the species • 

 themselves. The habits of these beetles, and the several distinct 



