26 DE. GLADSTONE ON THE EEFEACTION-EQUIYALENTS OE THE ELEMENTS. 
From N0 3 N=5-3 
„ N0 2 N=5\3 
Silicon . — From the tetrachloride, Si=T*5. Silicic acid, Si0 2 , in the form of quartz 
has the refraction-equivalent 1 2 - 4 and 12-6 for the ordinary and extraordinary rays 
respectively ; as deduced from silicic ether it is 12‘6, and from the soluble silicates 
12 ’6. Therefore Si = 6 *8. 
Boron.- — B 2 0 3 , as deduced from boracic ether, is 16"45, from crystallized borax 
16-85, and from borax in solution 16-7. Taking the mean of these values, 13 = 4-0. 
Zirconium . — From zircon, Zr=20"8 or 22-6, according as we reckon from the ordinary 
or extraordinary ray. 
Fluorine . — From potassium fluoride F=F45. The numbers given for fluor-spar and 
kryolite confirm this very small value, or rather indicate that this body has scarcely any 
influence on the rays of light. 
Summary. 
The general results of the foregoing deductions give the following numbers as the 
refraction-equivalents of the elements, already determined more or less accurately. 
Element. 
Atomic 
weight. 
Refra ction-equi valent. 
Specific refractive 
energy. 
Aluminium 
27-4 
8-4 
0-307 
Antimony 
122 
24-5? 
0-201 ? 
Arsenic 
75 
15-4 (other values?) 
0-205 
Barium 
137 
15-8 
0-115 
Boron 
11 
4-0 
0-364 
Bromine 
80 
15-3, in dissolved salts 16"9 
0-191 or 0-211 
Cadmium 
112 
13-6 
0-121 
Cassium 
133 
13-7 ? 
0-103? 
Calcium 
40 
10-4 
0-260 
Carbon 
12 
50 
0-417 
Cerium 
92 
13-6? 
0-148? 
Chlorine 
35-5 
9-9, in dissolved salts 10‘7 
0-279 or 0-301 
Chromium 
52-2 
15'9 (in chromates 23?) 
0-305 or 0-441 ? 
Cobalt 
58-8 
10-8 
0-184 
Copper 
63-4 
11-6 
0-183 
Didymium 
96 
12-8? 
0-133 ? 
Fluorine 
19 
1-4? 
0-073 ? 
Gold 
197 
24-0? 
0-122? 
Hydrogen 
1 
1-3, in hydracids 3'5 
1-3 or 3-5 
Iodine 
127 
24’5, in dissolved salts 27'2 
0-193 or 0-214 
Iron 
56 
12-0 in ferrous, 20- 1 in ferric salts 
0-214 or 0-359 
Lead 
207 
24-8 
0-120 
Lithium 
7 
3-8 
0-543 
Magnesium 
24 
70 
0-292 
Manganese 
55 
12-2 (26'2 ? in permanganate) 
0-222 or 0-476? 
Mercury 
200 
20-2? 
o-ioi? 
Nickel . 
58-8 
10*4 
0-177 
Nitrogen 
14 
4T, or 5 ’3 in higher oxides 
0-293 or 0-379 
Oxyg en 
16 
2-9 
0-181 
Palladium 
106-5 
22-4 ? 
0-210 ? 
Phosphorus 
31 
18-3 (other values?) 
0-590 
Platinum 
197-4 
26-0 
0-132 
Potassium 
391 
8-1 
0-207 
Rhodium 
104-4 
24-2? 
0-232? 
Rubidium 
85-4 
14-0 
0-164 
Silicon 
28 
7 - 5 ? (6-8 in oxygen compounds) 
0-268 ? or 0-243 
Silver 
108 
15-7 5 
0-145? 
Sodium 
23 
4-8 
0-209 
Strontium 
87-5 
13-6 
0-155 
Sulphur 
32 
16-0 (other values ?) 
0-500 
Thallium 
204 
21-6? 
0106? 
Tin 
118 
19-2? 
0-163 ? 
Titanium 
50 
25-5? 
0-510 ? 
Vanadium 
51-2 
25-3? 
0-494 ? 
Zinc 
65-2 
10-2 
0-156 
Zirconium 
89-6 
210? 
0-234 ? 
