SPECIFIC GRAVITY AND DISPLACEMENT OF SOME SALINE SOLUTIONS. 209 



S 126. In discussing the results of observation it is convenient to arrange them in a 

 more articulate form than that of Table II. 



The group of salts which forms the subject of these experiments is one of the most 

 remarkable in nature. The salts are nine in number and include all the possible binary 

 combinations of the members of the electro-positive triad K, Rb, Cs with those of the 

 electro-negative triad CI, Br, I. The two triads of simple bodies make three triads, 

 or one ennead, of binary compounds. The relations of the different members of the 

 ennead are shown in Table III,, in which the different features of the salts are exhibited 

 in separate sub-tables. In these sub-tables the data referring to salts of the same 

 metal (M) are found in the same column under the symbol for the metal (K, Rb, Cs), 

 and those relating to salts of the same metalloids (R) are found in the same line opposite 

 the symbol for the metalloid (CI, Br, I). The symbol MR is used to represent both 

 the formula and the molecular weight of the salt. 



Sub-table (a) of this table contains the formula and sub-table (c) the molecular 

 weight of each salt. The latter is the fundamental attribute of a substance, on which 

 all its properties depend. The molecular weights of the salts which occur in one 

 column differ by the amount of the difference of the atomic weights of the metalloids 

 which they contain, that is, by 44 '5 or 47. Similarly, contiguous salts in one line have 

 molecular weights which differ by 46 "4 or 47 '5. If we consider the two diagonal triads 

 in the ennead, we see that they are characterised by the fact that both the elements 

 in each unit are different from those in either of the other units. Further, along the 

 diagonal KCl-CsI the molecular weights of the units differ as much as possible from 

 each other, while the atomic weights of the components of each unit are as nearly as 

 possible identical, being close neighbours in the atomic series. On the other diagonal, 

 KI-CsCl, the molecular weights of the units agree with each other as nearly as possible, 

 while the atomic weights of the constituents of the units differ from each other as much 

 as possible. 



In sub-table (b) we have the values of T, the temperature at which the crystals 

 and mother-liquor of each salt were in equilibrium, and that at which the various 

 displacements were observed. 



Under the experimental conditions, which have been minutely described above, it 

 is impossible to fix in advance the exact temperature of equilibrium of the crystallising 

 liquid. This is given by the meteorological conditions, modified by the structural 

 features of the laboratory and of the apartment or enclosure where crystallisation 

 takes place. 



§ 127. The Crystal. — In compartment (g) we have the values of D, or the specific 

 gravity of the salt in crystal at T, referred to that of distilled water of the same 

 temperature as unity. The data in this compartment are in most cases for different, 

 but always neighbouring, temperatures. The differences of the values of T are, how- 

 ever, so small and those of D are so great that we may discuss the specific gravities 

 as if they had been made at one common temperature. 



TEANS. KOY. SOC. EDIN., VOL. XLIX., PART 1. (NO. 1). 27 



