Refraction of Fluorine. 



483 



the line A, and the last column contains the value for fluorine 

 obtained by deducting the amount due to the other elements, 

 viz. 35*556 for the water, 7*4 for the silicon, 11*5 for copper, 

 9*9 for nickel, 9*8 for zinc, 6*7 for magnesium, and 11*5 for 

 manganese, and then dividing the residue by six. The 

 refraction-equivalents for the above-named elements are taken 

 from the revised list published in the i American Journal of 

 Science ' for January 1885. 



Substance. 



Specific 

 gravity. 



Index, 

 F. 



Index, 

 A. 



Refraction- 

 equivalent, 

 A. 



Refraction- 

 equivalent 

 ofFluorine. 



CuF 2 ,SiF 4 ,6H 2 0... 

 NiF 2 ", SiF 4 , 6H 2 ... 

 ZnP a . SiF 4 , 6H 2 ... 

 MgF 2 ,SiF 4 ,6H 2 0... 

 MnF 2 , SiF 4 , 6H 2 0... 



2-182' 

 2-109 

 2-104 

 1-761 



1-858 



1-4131 

 1-4027 

 1-3926 

 1-3553 

 1-3690 



1-4049 

 1-3935 

 1-3857 

 1-3493 

 1-3621 



58-16 

 57-60 

 57-80 

 54-35 

 59-44 



062 

 079 



0-84 

 0-78 

 083 



Four out of the five will be seen to give closely accordant 

 results, and agree well with the general average, which is 0*77. 



The same observers give similar data for a silico-ammonio- 

 fluoride, 2NH 4 F, SiF 4 , which is a uniaxial crystal. The 

 index for the line F is 1*3723, and the calculated figure for 

 the line A is 1*3670. The specific gravity being 1*970, the 

 refraction-equivalent will be 33*16. The latest estimate for 

 NH 4 being ll'l, there will be 3*56 left to satisfy the six atoms 

 of fluorine, after deducting what may be due to the other 

 elements. This gives 0*59 for fluorine ; which is, as near as 

 possible, the mean of all the observations here examined. 



This still leaves a range of from 0*3 to 0*8 ; but in any case 

 the refraction-equivalent is of exceedingly small amount ; and 

 the specific refraction, even at the highest limit, can scarcely 

 be the half of that of any other substance known. Thus, 

 while the specific refraction of chlorine, bromine, and iodine 

 amounts to 0*279, 0*191, and 0*193 respectively, that of 

 fluorine will lie between 0*015 and 0*044, as calculated from 

 the extreme results of the observations recorded above. 



