20 EE. GLADSTONE ON THE REFRACTION-EQUIVALENTS OF THE ELEMENTS. 
Deductions. 
Carbon . — Crystallized carbon (that is diamond) has a refraction-equivalent of about 5*0 ; 
the same number was arrived at by Landolt from a consideration of a multitude of 
organic substances. If tve compare together the two gaseous oxides, CO, 7 ’53, and 
CO.,, 1(M)3, it is clear that the second atom of oxygen is represented by 2*5, and taking 
the first atom at the same it leaves 5*03 for carbon. 
If, indeed, anything is certain in this whole subject, it is that carbon, whether pure or 
in combination with other elements, and thus forming solid liquid or gaseous bodies, 
exerts the same influence on the rays of light transmitted by it, and that this influence 
may be expressed by the number 5-0; but the cumulative evidence on which this con- 
viction rests is derived from the whole range of organic bodies, and from many other 
compounds of carbon that will be considered under other headings. The apparent 
exceptions, such as the aromatic series of organic compounds, may be accounted for by 
a part of the hydrogen having a higher refraction-equivalent than it usually exhibits*. 
Hydrogen . — According to Dulong’s observations hydrogen gas has a refraction-equi- 
valent of T53, and it seems to have the same in water ; Landolt, however, has shown that 
in the large majority of the organic compounds examined by him, it does not exceed T3. 
This is confirmed by such observations as those on the new ketones, or on laurostearate 
of ethyl, given in Table III. Landolt examined no hydrocarbons, but assuming C = 5‘0, 
the series in Table II. give the following values for H : — 
Olefiant Gas .... gives 
1*27 
Amylene „ 
1*26 
Oil of Turpentine ... „ 
1*43 
Hydride of (Enanthyl . „ 
1*25 
Hydride of Capryl . . ,, 
1*27 
This is the value of IT in acetic, formic, tartaric, and oxalic acids ; but from Table VI. 
it would appear that the hydrogen in hydrochloric, hydrobromic, and hydriodic acids 
has a value about 2 '2 higher than in these organic acids ; it must therefore be about 3*5. 
The same element in nitric and sulphuric acids seems to have a value intermediate 
between these. 
Oxygen . — Gaseous oxygen, according to Dulong, is 3*04; and Landolt found that 3*0 
suited well for calculating the refraction-equivalent of the great group of organic com- 
pounds. There is, however, more uncertainty about this number; most of the sub- 
stances examined by the German professor contained comparatively little of the element, 
and his best comparisons give a somewhat lower figure. 
Assuming C = 5*Q, and 11 = 1*3, 
Sugar .... 
. . gives 0 = 2*8 
Carbonic Acid . 
. . „ 0 = 2*5 
Carbonic Oxide 
. . „ 0=2*5 
Oxalic Acid . 
G 
cTj 
II 
O 
* See Postscript. 
