ThermocJiemical Constants. 55 



The symbols refer to molecular oxygen and hydrogen, and 

 solid iodine. 



Now when we come to consider what the real reactions 

 taking place in the two cases are, namely : — 



(a) 2(I,0 8 ,H) + 2(I0 3 H,aq.) -I, I r 3(0, 0)-H, H- 



heat of fusion of 254 grams iodine + heat of lique- 

 faction of 96 grams oxygen and 2 grams hydrogen, 

 (6) 1, 0„ H 5 + IO,H„ aq. -i (I, I) - 3(0, 0) - 2| (H, H) 

 — heat of fusion of 127 grams + heat of liquefaction 

 of 96 grams oxygen and 5 grains hydrogen, 



it is impossible to see how the algebraic sums of these various 

 chemical and physical quantities can be multiples in the pro- 

 portion of 3 : 5, or in any other proportion, of any common 

 constant, unless it be by mere chance ; nor can the case be 

 simplified by regarding periodic acid as formed by the direct 

 substitution of H 3 for I, which it certainly is not. 



The instances brought forward by Thomsen of numbers 

 wliich are multiples of constants may be classed under three 

 heads : — 



A.- The heat of formation of compounds from their consti- 

 tuent elements, either in the presence of excess of water or 

 otherwise. 



(1) Iodic and periodic acids quoted above. 



(2) 2N0, 0, aq. = 36,330 = 1 x 36,330, 

 2N 0, 8 , aq. = 72,970 = 2 x 36,485. 



(3) P, 4 , H 3 * = 300,080 = 4 x 75,020, 

 P,0 3 ,H 3 =224,630 = 3x74,877. 



(4) S,0 2 = 77,280= 6x12,880, 

 S,0 3 =103,240= 8x12,905, 

 S, 4 , H 2 = 192,920 = 15 x 12,861. 



(5) 2S0 2 aq., = 53,520, 

 2S 2 2 aq., = 53,490. 



(6) 2CO,0,aq. =73,920, 

 CO,0,aq. =73,840. 



(7) Sn, 2 , H 2 O = 133,500 = 2 x 66,750, 

 Sn,0,H 2 = 65,410 = 1x65,410. 



* This refers to the heat of formation of the molten acids; the numbers 

 obtained with solutions of the acids are 4x76,320 and 3x75,860 respec- 

 tively, but these can scarcely be regarded as forming an independent 

 instance. The heat of dissolution of the two molten acids are naturally 

 positive quantities not differing much from each other, and both very 

 small in comparison with the heat of formation of the acids. 



