1868.] Dr. Gladstone on Refraction-Equivalents. 



441 



and the refractive index and density of the solution were taken. From 

 these was reckoned the refraction-equivalent, and subtracting from this 7i 

 times the refraction-equivalent of water for the solar line A, there remained 

 the refraction-equivalent of the dissolved salt for that part of the spec- 

 trum. That this fairly represents the action exerted on light by the 

 chemical compound itself is supported by several considerations. 1st. In 

 the few cases, such as chloride of sodium and sugar, where the refraction- 

 equivalent of the substance has been obtained, both in the solid and 

 dissolved condition, it is found to be the same. 2nd. Solutions of several 

 organic substances, such as formic and citric acids, give the theoretically 

 correct equivalent for these substances. 3rd. The refraction-equivalent of 

 a salt seems to be the same, whether it be dissolved in water or in alcohol. 

 4th. The refraction-equivalent of a salt in solution is not affected by 

 altering the amount of water in which it is dissolved. 5th. The numbers 

 reckoned for these salts in solution bear such a remarkable relation to one 

 another as to force the conviction that they are made up of two compo- 

 nents, the one depending on the metal, the other on the substance com- 

 bined with it. To exhibit the nature and force of this argument, it would 

 be necessary to tabulate a long series of results ; but for the present I 

 shall confine myself to the salts of potassium and sodium with the corre- 

 sponding hydrogen compounds. 



Dissolved compound. 





Refraction-equivalents. 



jQ 



1 ^ 











« § 1 



© s s 



3 



snce betwe 

 sium and ' 

 n compou 



Common 

 formula. 



li 



•puno 



gen 

 ound. 





1 g 



diuD 

 ompi 



Hydro 

 comp 



Differe 

 potasj 

 dium 



ffere 

 otass 

 roge 





l§ 





 m 



P 



MCI 



18-44 



15-11 



14-44 



3-3 



4-0 



MBr 



25-34 



21-70 



20-63 



3-6 



4-7 



MI 



35-33 



31-59 



31-17 



3-7 



4-2 



MNC 



17 12 











MSNC 



33-40 











MNO3 



21-80 



18-66 



17-24 



3-1 



4-5 



MPO3 





19-48 



18-68 







MHO 



12-82 



9-21 



5-95 



3-6 



6-8 



MCHgO 



27-68 



24-28 



20-89 



3-4 



6-8 



MC'HO., 



19-93 



16-03 



13-40 



3-9 



6-5 



MCHgO,, 



27-(35 



24-05 



21-20 



3-6 



6-5 



M^c^H^o; 



57-60 



50-39 



45-18 



3-6 



6-2 



M2CO3 



34-93 



28-55 





3-2 





M.,SO, 



30-55 



26-20* 



22-45 



2-2 



*4-l 



M.;Cr,0, 



79-9 



72-9 





3-5 





m;ph,o. 



26-94 



20-93 





3-0 





Chloride... 



Bromide 



Iodide 



Cyanide 



Sulphocyanide 



Nitrate 



Metapbosphate 



Hydrate 



Alcoliolate 



Formiate 



Acetate 



Tartrate 



Carbonate 



Sulphate 



Bichromate . . . 

 Hypophosphite 



From the above numbers several conclusions may be safely drawn. First, 



This number seems to bo too high, but it is the mean of fairly accordant results. 

 It is rejected in the calculation of average difference between potassium and sodium. 



