192 Mr. W. W. J. Nicol on the Molecular 



knowledge of the constitution of solutions ; that is, we find 

 that so long as the acid is a solid crystalline substance, the 

 value (H — K) = l and (H— Na) = ll'3. But when we have 

 to do with a liquid or gaseous acid this constancy of difference 

 disappears ; it reappears, however, when we contrast the 

 volume of the acid salt with that of the normal. 



KHS0 4 .... =1841-3 

 K 2 S0 4 =1840-1 



(H-K) .... =- 1-2 

 or 



NaHS0 4 1830-6 



Na 2 S0 4 1819-3 



(H-Na) .... = 11-3 



Thus it is seen that the replacement of the first H in H 2 S0 4 

 by K = 6*4 orNa= —4*3, while that of the second by K= —1*2 

 and by Na=ll*3, owing to the change of character of the 

 sulphuric acid from a liquid dissolved in water to a solid body 

 dissolved. Where the acid is solid no such difference between 

 the first and second atoms of hydrogen is to be detected, if we 

 except the difference 11'7, 11*0 in the case of the first and 

 second hydrogen atoms in tartaric acid ; a difference corre- 

 sponding to the difference in heat of neutralization observed 

 by Thomsen*. 



We have seen that water of constitution in solution occupies 

 a volume greater than that of water of solution ; but a com- 

 parison of the sodium phosphates in Table II. shows that the 

 elements of water in a molecule occupy less volume than water. 

 Thus:— 



JSTaPO 3 301H 2 O .... =5441-1 

 NaH 2 PO 4 300H 2 O . . . =5431-2 



- ~9^ 

 and 



Na 4 P 2 O 7 401H 2 O .... =7231-5 



2(Na 2 HPO 4 )400H 2 O . . . =7217-6 



- 13-9 



according to whether the elements of water are contained in 

 one molecule or in two. 



To return to water of constitution and crystallization. 



* Thermoch. Untersuch. vol. i. pp. 279 &c. 



