Dr. Gladstone on Refraction-Equivalents. 



81! 



exert very nearly, if not precisely, the same effect on the velocity of 

 the rays of light. 



Another deduction from the above Table is that already alluded 

 to in regard to hydrogen ; while in the organic acids it probably has 

 the known refraction-equivalent 1*3, it would seem that in the others, 

 viz. hydrochloric, hydrobromic, hydriodic, nitric, metaphosphoric, 

 and sulphuric acids, it has a very much higher refraction-equivalent, 

 one in fact which is little less than sodium, and falls short of potas- 

 sium by only about 4*3. Hence we may we deduce — 



Hydrogen in organic compounds =1*3 



Hydrogen in mineral acids =3*7 



How far this conclusion may hold good throughout, and whether 

 one number should be an exact multiple of the other number, must 

 remain to be determined by future observations. It appears, how- 

 ever, to answer in the affirmative the question whether an element 

 can have more than one definite refraction-equivalent. 



Of course, from the Table given above, it would be easy to 

 deduce values for each of the electro-negative constituents ; but it 

 would be safer to generalize from a larger number of instances. 



The series of observations on potassium and sodium salts are the 

 most complete and the most carefully revised of any which have yet 

 been made ; but if their refraction-equivalents are fixed, it becomes 

 a much simpler matter to determine those of most other metals. 

 Thus, of lead the nitrate and acetate have alone been examined ; but 

 as the refraction-equivalents reckoned for these salts differ from 

 those of the corresponding potassium compounds in each instance 

 by 4*1, the presumption is great that the refraction-equivalent of 

 lead is very near 8'0 + 4-l, or 12'1. 



The following are numbers deduced from two or more salts of 

 each metal. They must be looked upon only as approximately true ; 

 and any subsequent modification of the value 8*0 for potassium 

 must lead to a corresponding modification of the whole series. 



Metal. 



Chemical 

 equivalent. 



Eefraction- 

 equivalent. 



Specific 



refractive 



energy. 





39 

 23 

 7 

 12 

 68-5 

 43-8 

 20 

 32-6 

 29-5 

 29-4 



103-5 



100 



8-0 

 4-6 

 3-9 

 3-7 

 7-8 

 6-5 

 5-2 

 4-8 

 51 

 52 

 121 

 9-8 



0205 

 0-200 

 0-557 

 0-308 

 0-114 

 0-148 

 0260 

 0-147 

 0-173 

 0-177 

 0117 

 0-098 

















Nickel 



Cobalt 





Mercury 





18 



11-4 



0-633 





