March 17, 1870] 
NATURE 
519 
and which is expressed in the language of opticians as w#—1. 
This energy divided by the density, that is “=" is called the 
cf 
‘specific refractive energy,” and is, in the case of liquids, a 
constant, not affected by temperature. This conclusion was sub- 
sequently confirmed by the experiments of Landolt, Wiillner, 
and Kiihlman. As to the second line of research, that of the 
refraction of mixtures, solutions, and simple combinations, the 
conclusion was arrived at that here also the nearest approxima- 
5) 
: : uw—1 ‘ F 
tion to the truth was given by ——, and this conclusion has been 
§ y 7? 
a 
fully confirmed by the careful experiments of Wiillner. The 
same general expression holds good also in the case of a gas 
or asolid in solution, and, indeed, it was expected to be so, for 
water, phosphorus, and sulphur have the same energies in the 
liquid and solid states. The question now presented itself, does 
an elementary substance retain its specific power of retarding 
rays when it is combined chemically with other elements? An 
affirmative reply was suggested by many considerations, It 
was, for instance, found that bromoform (CH Brg) and bibromide 
of bromethylene (C,H,Br;) have almost the same specific refrac- 
tive energy as bromine itself. On the other hand, however, the 
investigators observed that isomeric liquids were not always 
identical in refractive energy, and that the replacement of hydro- 
gen by oxygen in organic compounds effected a much greater 
optical change in some instances than in others. Hence the con- 
clusion was drawn that the specific refractive energy of every 
liquid is composed of the specific refractive energies of its com- 
ponent elements, modified by the manner of combination. The 
third line of research was that of the refractions of different 
homologous compounds. The experiments of Delffs, of Landolt, 
and of Gladstone and Dale, have led to the view that in all 
the series containing the radicals, methyl and its congeners, the 
specific refractive energies increase as the series advances, and 
that the amount of optical change is less between the higher than 
between the members of the lower series. Landolt, adopting 
Gladstone and Dale’s formula for the specific refractive energy, 
multiplied it by the atomic weight P ; and this P “ot he desig - 
nated the “ Refraction Equivalent.” According to this represen- 
tation, the refraction equivalent of a body is the sum of the 
refraction equivalents of its constituent elements. The great 
advantage of this kind of expression is, that it permits of the 
easy comparison of the optical properties of different substances. 
By making these comparisons, Landolt found that the refraction 
equivalent of carbon is 50; that of hydrogen, 1°3 ; and that of 
oxygen, 30. Direct experiments have given figures very close 
to these. The way of calculating the refraction equivalent of a 
compound from these data may be illustrated by ether. C Hy, 
O=4 (50) + 10 (1-3) + 3°0=36'0. The refraction equivalent 
deduced from observation is 36°26. A great variety of liquids 
have given the same equivalents by calculation as by direct inves- 
tigation. Yet there are exceptions to this agreement with theory. 
The whole group of the aromatic hydrocarbons and their deriva- 
tives give refraction equivalents much above the calculated 
numbers. This anomaly must be due to an erroneous represen- 
tation of the constitution of their nucleus, which cannot be 
greater than C;H,. However, the above method makes it pos- 
sible to find the refraction equivalent of bodies, which could not 
otherwise be taken; for instance, of metals. The refraction 
equivalents of fifty elements have been determined in this way. 
It is to be remarked that the figures in the following list repre- 
sent A of the solar system :— 
Aluminium . 8-4 Todine 5 .  24°5—27°2 
Barium Z » 15°78 Tron . ‘ . 12'0—20°1 
Bromine . + 15°3—16'9 | Lead. : - 24°8 
Calcium. » 1074 Magnesium 70 
Carbon c 1500 Manganese 12‘2—26'2 
Chlorine. - 9'99—10°7 | Mercury . . 21°3—29'0 
Chromium . . 15°9—23'0 | Nitrogen . a) Pasr== 9573 
Copper : 5 TG Oxygen. C250 
Hydrogen . »  1°3— 3°5 | Phosphorus ae eee) 
Platinum. » 2650 Sodium. CaS 
Potassium . i Sulphur. 16°0 
Silicon ; » 75— 68) Tin . z + 27°0=—19'2 
Silver 13°5 Zinc . 5 Se becky} 
It will be seen that some of the elements have a double value, 
and this peculiarity is in most cases coincident witha change of 
atomicity. Thus, iron in the ferrous salts has the equivalent 
120, in the ferric salts 201, and since the refraction equivalent 
of iron in potassic ferridcyanide is 11°7, the view suggests itself 
that the metal is here in the same condition as in the ferrous 
salts. Great anomalies, however, present themselves in the case 
of oxygen. Its equivalent in many compounds is 29, but in 
others it comes down to 2'1, and in some cases, as in sulphates 
and phosphates, it would seem to be a negative quantity. This 
points to the conclusion that oxygen has the power of greatly 
modifying the action on light of those elements with which it is 
combined in a high proportion, On looking over the above list 
one is struck by the identity of the equivalents of those elements 
which have the same, or nearly the same, atomic weight. This 
property is still more prominent when the specific refractive ener- 
gies of the elements instead of their refraction equivalents are 
considered. The following pairs may be noted in this respect :— 
Tron, o'214 Aluminium, 0°307 Bromine, o'19% 
Manganese, 0°222 Chromium, 0'305 Iodine, 07193 
But the most suggestive comparison is that between the specific 
refractive energy and the combining proportions of those metals 
that form salts not decomposable by water. By combining 
proportion is meant the actual amount which will combine with 
a certain quantity of a salt radicle. A few of these metals may 
be quoted here :— 
Specif. refi. Combining 
energy. proportion. 
Hydrogen . . . 1300 I 
Albuminium . . 307 9 
Galcium)., Fv. 3, 260 20 
Tnopyorie + Svensh ee eet: 23 
Sodium) = 4 5 + 209 23 
Potassium *. . . 207 39°1 
Goppert a) x). 183 Bley 
Silven-nu-a 3) 125 108 
Ibead® i 518 120 103°5 
&e. 
The regularity in the decrease of the numbers in the first 
column and the corresponding increase in the second column 
would suggest that the combining proportions of Silver, Lead, 
&c. ought to be halved in order to bring those elements to 
about their right places in the list. There is further a re- 
markable coincidence between the power of a metallic element 
to refract the rays of light, and its power to saturate the 
affinities of other bodies ; of course, it must be borne in mind 
that a small combining proportion means a high saturating 
power, 
; The names of the officers proposed by the Council of the 
Chemical Society for election on the 30th March, are :—Pre- 
sident: A. W. Williamson. New Vice-Bresidents; IE. Frank- 
land, A. Matthiessen. New Members of Council: H. Bassett, 
F. Field, F.R.S. ; M. Holzmann, Ph.D.; W. J. Russell, Ph. D.; 
R. Angus Smith, Ph.D., F.R.S.; John Tyndall, LL.D., F.R.S. 
Entomological Society of London, March 7.—Mr.F. P. 
Pascoe, vice-president, in the chair. The Rey. R. P. Murray 
and M. J. C. Puls were elected members. Professor West- 
wood exhibited a number of old locusts, with a view to deter- 
mine what is the true Locusta migratoria of Linneus. The 
Rev. H. S. Gorham sent for exhibition specimens of Szezeces 
neglectus, a beetle new to Britain, but probably confused in col- 
lections with S. azgwstatus. Mr. Albert Miiller exhibited a 
curious acorn-like gall formed on the mid-rib on the underside 
of the leaf of a species of Gretwm. Mr. Janson exhibited a 
large number of butterflies collected by his son in Nicaragua in 
November and December last. Mr. Butler exhibited specimens 
of Areynnis Adippe and Niobe, in support of his previously 
expressed opinion that the two forms are but one species. Dr. 
Wallace exhibited dark varieties of AZe/itea Athalia, and speci- 
mens of Herminia derivalis. Mr. Stainton exhibited Cosmo- 
pteryx Sienigiela, bred in this country from Russian larva: which 
fed in reeds. Dr. Wallace exhibited cocoons and silk of several 
species of silk-producing moths, and addressed the meeting on 
the progress and science of Sericiculture in this country and in 
the colonies. The following paper was read: ‘‘ Descriptions of 
twelve new exotic species of the Coleopterous family Prelaphide,” 
by Professor Westwood. 
Ethnological Society, March $8.— Professor Huxley, F.R.S., 
president, in the chair. Captain Campbell, R.E., was announced 
as a new member. Colonel Lane Fox read a paper ‘‘ On the 
opening of two caims near Bangor, in North Wales.” One 
was situated on the summit of Moel Faban, and contained a 
