38 Proceedings of the Royal Society of Edinburgh. [Sess. 
The results of the measurements made in the visible and infra-red 
regions of the spectrum are given below in Tables Ia. and Ib. The numbers 
Table Ia. — Values of A obtained with the Spectrophotometer. 
A. 
Fe 2 Cl 6 
.12H 2 0. 
Fe 2 Br 6 . 
Fe 2 (N0 3 ) 6 .18H 2 0. 
Fe 2 (S0 4 ) 3 . 
FeCl 2 . 
FeS0 4 .7H 2 0. 
c= 1 *0. 
c= T. 
c = 1 *0. 
c = -5. 
c = T. 
c = l* 0. 
c = T. 
c = T0. 
c = T. 
<;=4-0. 
c = T0. 
Ci 
II 
© 
*434 u 
37*2 
105 
7-3 
10-6 
6-9 
9-5 
•75 
•30 
•22 
•444 
25T 
89 
9-6 
33 
6*3 
•46 
•26 
•20 
•453 
16-5 
71 
5-5 
8-6 
2T 
4'7 
•31 
•21 
T6 
•463 
10-6 
58 
7-5 
1*7 
3-9 
T9 
T7 
T4 
•475 
7-8 
43 
3-6 
6-5 
IT 
3-0 
T3 
T5 
•486 
6-2 
34 
5T 
•91 
2-5 
•076 
T3 
•499 
11 *4 
43 
24 
2*2*5 
4-04 
•76 
2-2 
•056 
Tl 
•514 
4-8 
3-0 
15 
2-81 
•71 
2T 
•041 
•085 
•098 
•529 
1*8 
2-0 
7-8 
1*6*3 
1-59 
•62 
T9 
•028 
•085 
•547 
•82 
1T5 
4-0 
•70 
•82 
1-6 
•025 
•063 
•058 
•563 
•46 
•76 
14-5 
2-2 
•40 
•50 
•51 
1-3 
•021 
•582 
•33 
•42 
1-05 
•26 
T7 
•73 
•026 
•054 
•602 
•29 
5-47 
•73 
T6 
•31 
•49 
•032 
•066 
•625 
•26 
2-96 
T2 
•23 
•29 
•042 
•069 
•080 
•653 
•22 
T9 
13*9 
T4 
T6 
•21 
•060 
•086 
T06 
•687 
T8 
•23 
6-4 
T7 
T9 
•091 
Tl 
T6 
717 
T6 
4-2 
... 
... 
T15 
•15 
•22 
Table Ib. — 
Values obtained with 
the Thermopile. 
•677 
T6 
6-0 
1-74 
•41 
T6 
T9 
•25 
TO 
T4 
T6 
•710 
T5 
•31 
3-9 
1-70 
•47 
T9 
•28 
•24 
•28 
T2 
T7 
•20 
•746 
■15 
•41 
1-66 
•58 
•25 
•37 
•33 
•37 
T7 
•20 
•25 
•788 
T7 
•49 
2-8 
1 *77 
•72 
•33 
•50 
•43 
•49 
•27 
•28 
•39 
•837 
•22 
•46 
2T0 
•94 
•32 
•45 
•51 
•64 
•50 
•50 
•70 
•900 
•23 
•39 
4*T 
2-48 
1-26 
•23 
•31 
•42 
•54 
•89 
•84 
1-26 
•968 
T9 
•28 
2-66 
1-22 
T3 
•21 
•29 
*41 
1T0 
1-00 
1-54 
1-062 
T2 
T2 
4-8 
2-38 
Til 
•04 
TO 
T3 
T8 
1T3 
1-02 
T62 
1T75 
•06 
T75 
•89 
•01 
•04 
•04 
•05 
1-00 
•95 
T39 
1*300 
T9 
1-21 
•64 
•84 
•82 
1T4 
given are the values of the molecular extinction coefficient A, defined by 
the equation 
I = I 0 lO~ Acd , 
where I 0 and I represent the intensities of light before and after passing 
through a thickness d of solution, of which c is the concentration expressed 
in gramme-molecules per litre ; each number is the mean of two or more 
values. In the case of the ferric salts, solutions of concentrations c = T0 
and c — T were examined. The solutions of the ferrous salts of concentra- 
tion c = T were almost colourless, and could not therefore be examined with 
