by Displacement in their own Mother-liquor. 33 



weight was used as a control. The result shows that the value 

 of Dj may be safely accepted. In case of potassium chloride 

 the value of D 3 (1*951) is accepted, and the reason for this is as fol- 

 lows : The first portion of salt was in very coarse powder, 

 and in mixing it with the mother-liquor numerous crystalline 

 particles were observed which contained gaseous enclosures, 

 easily perceptible by the naked eye. As was expected, the 

 observed specific gravity proved to be low. The second por- 

 tion was much more finely powdered and the specific gravity 

 resulting from the two was higher (1-8872). But this result is 

 affected to the full extent by the gaseous enclosures in the first 

 portion. We therefore calculate the specific gravity from the 

 second portion alone, which gives 1*9510 for the specific gravity. 



Discussion. — It is an advantage of the method just described 

 that it furnishes more than the mere determination of the 

 specific gravity of the salt. Thus, by ascertaining almost 

 simultaneously the specific gravity of the mother-liquor and 

 the displacement in it of the crystals, both being at the tem- 

 perature of equilibrium, data are obtained for the deter- 

 mination of the relation between the displacement of the 

 salt in crystal and its apparent displacement in saturated solu- 

 tion at that temperature. It has not hitherto been permissible 

 to make exact comparisons of this kind owing to the independ- 

 ence of the observations on the salt and on the solution, which 

 have been available. 



In discussing the results of observation it is convenient to 

 arrange them in a more articulate form than that of Table II 

 so as to bring each feature forward prominently and by itself. 



The group of salts which forms the subject of these experi- 

 ments 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, lib, 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 best shown in a table of the form of Table III. 

 In it the salts of the same metal, M, are all in one column, and 

 those of the same metalloid, R, all in one line. The symbol 

 MB represents both the formula and the molecular weight of 

 the salt. 



(a) 



* From the Greek hweaq, which, signifies a body of nine. 



Am. Jour. Scl— Fourth Series, Vol. XXI, No. 12].— January, 1906. 

 3 





Table III. 







Values of ME. 





K 



Kb Cs 

 Formula 





KC1 



RbCl CsCl 



CI 



KBr 



RbBr CsBr 



Br 



KI 



Rbl Csl 



I 



