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



In the case of the similar salts of potassium, 

 Mol. vol. K 2 C1 2 100 H 2 = 1857-1 

 „ „ K 2 S0 4 100 H 2 = 1840-1 



and 



(Cl 2 -S0 4 ) ; then, = 17-0 



K(ci-^ 4 ) = 8-5 = A, 



as before ; in a solution half the strength, 



k(c1-^M = 8-9=A. 



So that the difference in A for solutions of the same strength 

 is nil in the one case and *3 in the other — a difference of -goVo? 

 easily produced by the different solubilities (see loc. cit., where 

 this point is discussed). 



But in the case of the sodium salts an anhydrous one is 

 compared with a hydrated, while in the case of potassium 

 neither salt crystallizes with water. It thus appears that 

 water of crystallization has the same volume as water of 

 solution. Further evidence is given by the following : — 



(K-Na)-^ 4 A = 10'39; 



while (K-]N T a)Cl A = 10"15, . 



(K-Na)N0 3 A = 10'36, 



(K-Na)OH A = 10'06, 



(K-Na)ClOs A = 10-56. 



This result, that the presence or absence of water of cry- 

 stallization does not affect the molecular volume in solution, 

 appeared to me most striking and well worthy of further 

 investigation. I have therefore noted the number of molecules 

 of water of crystallization in the salts compared in the follow- 

 ing pages, and it will be found that the above statement is 

 correct. 



The evidence I have to bring forward in support of my 

 previous statement with regard to the constancy of molecular 

 or rather atomic volume exhibited by all elements and groups 

 of elements, consists of density determinations of nearly 

 50 salts, representatives of all the important classes from 

 monatomic up to triatomic acids. My former determinations 

 are here included, either as they stand or added into the 

 means. The results are given in one table, as before, for 

 convenience of reference, and subsidiary tables are formed 

 from it as occasion requires (Table II.). 



