DR. GLADSTONE ON THE RETRACTION -EQUIVALENTS OR THE ELEMENTS. 21 
Formic Acid . . . gives 0 = 3*1 
Tartaric Acid ... „ 0 = 2*9 
Citric Acid . . . . „ 0 = 2*9 
On comparing nitrate of potassium, KNO>, 22*11, with nitrite of potassium, KN0 2 , 19*31, 
we deduce for O the value 2*8. 
From this diversified evidence, 2*9 may be fairly taken as the probable value of 
oxygen. 
Sulphur. — The pure element, whether solid or liquid, has a refraction-equivalent of 
16*0 or 16*3; as deduced from CS 2 , 36*7, it will be 15*85. Again, the difference be- 
tween KCNS, 33*47, and KCN, 17*23, gives S=1G*24. ; it will be seen that it has a 
similar value in chloride of sulphur. It is evident, however, that in the two gases, 
H 2 S, 14*28, and S0 2 , 14*91, or in liquified S0 2 , 14*59, it cannot be 16 ; nor yet in its 
other oxygen compound, H 2 S0 4 , 21*9. 
Phosphorus. — The refraction-equivalent for this very dispersive elementary body is 
18*3 for the line A. In its compounds with the halogens it seems to exert the same 
influence on light, but in phosphoric acid its refractive energy must be greatly dimi- 
nished. 
Chlorine. — The gas itself has the refraction-equivalent of 8*87, as reckoned from 
Duloxg’s experiments, and the same figure represents it in gaseous phosgene ; but a 
somwehat higher number is arrived at when liquid compounds are examined. Thus, 
taking the numbers previously given for carbon, hydrogen, sulphur, and phosphorus, 
we find — 
From Tetrachloride of Carbon . . . Chlorine = 9*8 
„ Chloroform ,, = 9*6 
,, „ (Haagen) ... ,, = 9*7 
„ Bichloride of Chlorethylene . „ =9*9 
,, Chloride of Sulphur .... ,, = 9 ( 8 
„ Terchloride of Phosphorus . . ,, = 10*0 
„ Bichloride of Ethylene ... „ = 9*8 
„ Chloral „ =10*4 
Moreover the substitution of chlorine for hydrogen in benzole gives for each Cl — II 8*7, 
that is 0 = 10*0. The mean of these numbers is 9*9. 
Bromine . — The liquid element has a refraction-equivalent of 16*23. The determina- 
tions of compounds of carbon, hydrogen, and phosphorus give : — 
From Bromoform Bromine =15*7 
,, Bibromide of Bromethylene . „ =15*1 
„ Bibromide of Chlorethylene . „ =15*0 
„ Terbromide of Phosphorus . ,, =15*0 
., Bromide of Ethyl .... ,, =15*0 
„ Bromide of Amyl .... „ =15*7 
„ Bibromide of Ethylene . . „ =15*4 
The average of these numbers is 15*3. 
