531 
1910-11.] Absorption of Light by Inorganic Salts. No. II. 
of the nicol readings being 2 0 r The cells were then interchanged and 
the readings repeated, the difference of the two settings being now 2 0 2 . 
Then the value of A cd for the wave-length in question is given by 
. , , tan 0-, t cot 0-t 
A cd = log -± or log - 1 
6 tan 0 9 & cot 0 9 
according as 0 1 or 0 2 is larger. 
Readings were taken in this manner for different wave-lengths 
throughout the spectrum, care of course being taken that all the readings 
were independent. That is, the range of wave-lengths compared never 
overlapped for two adjacent points in the spectrum. 
In order to prevent error, solutions for each salt were made up at least 
twice, and for each salt three independent determinations of A cd were made 
throughout the spectrum. To give an idea of the accuracy usually obtained, 
all the determinations for the solution of cobalt nitrate are tabulated below : — 
A cd. 
A cd. 
A 
1st Set. 
2nd Set. 1 
3rd Set. 
Mean. 
A 
1st Set. 
2nd Set. 
3rd Set. 
Mean. 
434 [x/x 
•24 
•30 
•28 
•28 
547 
•61 
•74 
•69 
•68 
444 
•41 
•42 
•45 
•42 
563 
•36 
•30 
•35 
•34 
453 
•54 
•63 
*66 
•61 
582 
•20 
•17 
•12 
•16 
463 
•83 
•93 
•88 
•88 
602 
•] 3 
•10 
•10 
•11 
475 
1-06 
M3 
1-02 
1-07 
625 
•11 
•08 
•07 
•09 
486 
1-29 
1-34 
1-28 
1*30 
653 
•11 
•04 
•05 
•07 
499 
1*55 
1-55 
1-43 
1-52 
687 
•08 
•03 
•03 
•05 
514 
1-60 
1-62 
1-56 
1-60 
717 
•05 
'00 
•01 
•02 
529 
1-20 
1-31 
1-21 
1-24 
The following table gives the results for all six salts : — 
Values of A for Cobalt Salts in the Visible Spectrum. 
A. 
c= 075. 
Fluoride. 
c=-361. 
Chloride. 
c = ’303. 
Bromide. 
c= 077. 
Iodide. 
c=- 305. 
Nitrate. 
c=*306. 
Sulphate. 
424 / x/x 
... 
•68 
434 
•82 
1-19 
1-19 
•91 
106 
444 
1-10 
1-54 
1-80 
270 
1-39 
1-82 
453 
1-55 
1*99 
2-32 
20-2 
200 
2-55 
463 
207 
2*69 
3-26 
15-6 
2-91 
3 43 
475 
2-65 
3-29 
3-80 
110 
3-51 
402 
486 
308 
377 
3 89 
9-20 
4*29 
4-69 
499 
3-44 
400 
4-86 
707 
4-97 
5-53 
505 
5-16 
514 
357 
4*87 
5*18 
708 
5-23 
5-85 
529 
300 
3*82 
403 
5-86 
4-64 
4-70 
547 
1*75 
2-17 
1-94 
406 
2-24 
2-72 
563 
•80 
M3 
108 
2-72 
M2 
1-38 
582 
•43 
•64 
•45 
1-20 
•54 
•72 
602 
•35 
•44 
•33 
•95 
•37 
•56 
625 
•27 
•38 
•32 
•70 
•29 
•45 
653 
•31 
•35 
•25 
•60 
■22 
•35 
687 
•23 
•25 
•17 
•51 
•16 
•24 
717 
•15 
•11 
07 
•25 
