56 Prof. S. U. Pickering on 



(8) Fe, Cl 2 = 82,050 = 3 x 27,350, 

 Fe 2 , Cl 6 = 192,080 = 7 x 27,440*, 

 Fe 2 Cl 6 , aq. - 2(FeCl 2 , aq.) = 27,560. 



(9) Fe,0,H 2 = 68,280= 5x13,656, 

 Fe 2 , 3 , 3H 2 = 191,150 = 14 x 13,654. 



B. Differences between the heat of formation of analogous 

 compounds. 



(10) H 2 , Cl 2 -H 2 , Brf s = 19,480 = 3 x 6493, 

 H 2 ,Brf s -H 2 ,If as = 25,698 = 4x6425. 



(11) N, H 4 , CI - H, CI, aq. = 36,472, 

 N, H 4 , Br- H, Br, aq. = 36,972, 

 N,H 4 ,I -H,I,aq. =36,142. 



(12) P 2 ,0 5 =369,900 = 5x73,980, 

 As 2 , 5 = 219,380 = 3 x 73,130, 

 As 2 , O 3 =154,670 = 2 x 77,330. 



C. Numerical relations between similar reactions, and be- 

 tween the differences between similar reactions, where more 

 than one product is formed. 



(13) 6KOHaq. + 6Cl=3KClaq. +3KOClaq. + 3H 2 



= 73,855 = 3x24,618. 

 6KOH aq. + 6C1 = 5KC1 aq. + K0 3 C1 aq. + 3H 2 



= 97,945=4x24,486. 



(14) 2HC10 3 , 10HCI = - 30,920 132 440 _ 4 x 33 n(] 

 2HBrO 3 ,10HBr = 101,520 ^0-2x^675 

 2HIO 3 ,10HI = 166,870 ^ooll v 33 300 



H 5 I0 6 , 7HI = 133,570 d ^ oU0 " L x dd ' dUU * 



There is not one of these sets of quantities (except perhaps 

 the actions of chlorine on potash, 13, and the formation of the 

 haloid acids, 10) in which the actions compared are so simple 

 or so strictly analogous, that we might reasonably expect the 

 sum total to be made up of the same constants. 



In some cases, indeed, it is apparent that Thomson has been 

 led astray by his eagerness to discover the existence of simple 

 relations. Thus, in the case of 11, what possible meaning can 

 be attached to quantities obtained by subtracting the heat of 

 formation of aqueous solutions of the haloid acids from that of 



* In this and the following case Thomsen inserts two other quantities 

 which are multiples of the same constants, "but they are in reality (as he 

 shows) dependent on those given here. 



I have not inserted the case of marsh-gas and carbon tetrachloride, the 

 heat of formation of which is nearly the same ; this is a constant of a 

 different character and presents no difficulties. 



