ELECTIVE ATTRACTION. 



In the expression of compound affin- 

 ities, the sketches must either be made 

 from actual experiment in every instance, 

 or by deduction from the numerical ex- 

 pressions of the forces of attraction. 

 Some of the difficulties of effecting this 

 have been mentioned in the present arti- 

 cle ; but as a conjectural set of numbers, 



inferred from such facts as we possess, 

 may be useful, in many instances, to point 

 out the probability of decompositions pre- 

 viously to trial, Guyton Morveau's table 

 of the numerical expression of affinity 

 between the alkalies and soluble earths, 

 and the five principal acids, is herein 

 serted. 



TABLE VII. NUMERICAL EXPRESSION OF AFFINITIES. 



BT GUYTOIT MOB.VEAU. 



The method of exhibiting simple or 

 compound affinities by symbols, according 

 to Bergman, consists in placing those sub- 

 stances which are applied to each other 

 upon the same horizontal line of direc- 

 tion ; the component parts of the sub- 

 stances being placed at the two extremi- 

 ties of a vertical bracket ; and the new 

 products, if any, are placed one above the 

 other, at the middle part of a horizontal 

 bracket, connecting their component 

 principles. This will be rendered clearer 

 by an example. 



1. Suppose magnesia to be presented 

 to a solution of sulphat of potash, it will 

 be found that no decomposition takes 

 place. These facts are expressed as fol- 

 lows: 



("Potash 



Sulphat of I 



P tash (Sulphuric 



l_ acid Magnesia. 

 In the above scheme, the sulphat of 

 potash is placed opposite the point of a 

 vertical bracket; and its two component 

 parts, potash and sulphuric acid, are 

 placed within the extremities of the same 

 bracket. Horizontally opposite the sul- 



phuric acid is placed magnesia, to denote 

 that it is presented to that acid. And as 

 these two substances are not connected 

 by a bracket, it is to be understood, from 

 the scheme, that they do not unite, and 

 consequently that the sulphat of potash 

 remains undecomposed. 



II. On the contrary, if, to a solution of 

 sulphat of magnesia, potash be added, a 

 decomposition will ensue, which is ex- 

 pressed as follows : 



Sulphat of 

 magnesia 



fMagnesia 



ia * Su]p 

 [_ aci 



acid Potash 



Sulphat of potash 



The arrangements in this scheme de- 

 pend on the same principles as those of 

 the foregoing : but the bracket under- 

 neath the sulphuric acid and potash de- 

 notes, that these two substances unite, 

 and form sulphat of potash, which is ac- 

 cordingly placed beneath the middle of 

 the bracket. The point of the bracket 

 being turned up, is made to denote, that 

 the compound remains suspended, or in 



