DR. GLADSTONE ON THE REFRACTION-EQUIVALENTS OE THE ELEMENTS. 27 
In the above Table those equivalents are marked 1 where they have been deduced 
from only one compound, or where the different determinations are not fairly accordant. 
At some future time I hope to reexamine each of the doubtful points, and to extend 
the observations to the whole range of the chemical elements. The question of disper- 
sion-equivalents is also of interest : the data for an investigation of the matter are 
given in the Appendix, since the refractive index has been calculated for the lines D and 
H, as well as the line A ; but I have avoided encumbering the present paper with any 
remarks on this subject. 
The specific refractive energy of a body is in some respects worthy of more considera- 
tion than the refraction-equivalent, for it is a physical property independent of chemical 
theories. If these energies in the preceding Table are compared with one another 
several suggestive facts may be observed. 
1st. Hydrogen has more than double the energy of any other element, even in the 
lowest number that can be assigned to it. 
2nd. Phosphorus, vanadium, titanium, and sulphur have singularly high energies, 
and they are substances that present certain chemical analogies. 
3rd. There are several pairs of analogous elements having the same, or nearly the 
same, energy ; thus, bromine and iodine, arsenic and antimony, potassium and sodium, 
manganese and iron, nickel and cobalt. 
4th. An element in altering its quantivalence alters its energy. 
5tli. If those metals that form the soluble salts of Table V. be arranged in the order 
of their energies, it will be seen that, with a few exceptions, they are in the inverse order 
of their combining proportions. This is shown in the annexed Table, where the third 
column gives the actual weight of the metal that combines with 35 *5 of chlorine. 
Element. 
Specific 
refractive 
energy. 
Combining 
proportion. 
Hydrogen 
1-300 
1 
Lithium 
•510 
7 
Aluminium 
•307 
9-1 
Chromium 
•305 
17-4 
Magnesium 
•292 
12 
Calcium 
•260 
20 
Zirconium 
•234? 
22-4 
Rhodium 
•232 ? 
34-8 
Manganese 
•222 
27-5 
Iron 
•214 
28 
Palladium 
•210? 
532 
Sodium 
•209 
23 
Potassium 
•207 
39 1 
Cobalt 
■184 
29-4 
Copper 
•183 
31-7 
Element. 
Specific 
refractive 
energy. 
Combining 
proportion. 
Nickel 
•177 
29-4 
Rubidium 
•164 
85-4 
Zinc 
32 6 
Strontium 
•155 
43-8 
Cerium 
T48? 
46 
Silver 
•145 ? 
108 
Didymium 
•133? 
475 
Platinum 
•132? 
49-3 
Gold 
•1227 
65’7 
Cadmium 
■121 
56 
Lead 
•120 
103-5 
Barium 
•115 
68-5 
Thallium 
•106? 
204 
Caesium 
•103? 
133 
Mercury 
•101? 
100 
This has not the regularity of a physical law, but it clearly points to some connexion 
between the power of a metallic body to saturate the affinities of other elements, and its 
power to retard the rays of light. 
