OF ZINC AND ANTIMONY. 367 



of the planets prove that the force of gravitation exerted by the sun has been disturbed 

 in its action by the influence of the other members of the system. As the details in 

 the form of the curve have been fully discussed in the previous part of the memoir, it 

 does not seem to be necessary to dwell upon this argument, and I would therefore, 

 without further comment, offer the curve as it has been laid down on the plate, as the 

 proof of the validity of the explanation of the variation in composition here advanced. 



It is worthy of remark, that, while the curve of variation may be said almost to de- 

 monstrate that the law of definite proportions may be disturbed in its action, it also 

 most clearly sustains the integrity of the law itself; for, as may be seen on inspection, 

 the chemical force is sufficiently strong to retain the curve of SbZn^ parallel to the axis 

 of ordinates through a variation in the menstruum of nearly five per cent, and it is only 

 when the excess of antimony present in the alloy exceeds six per cent that the force 

 which it exerts becomes strong enough to disturb the action of the law. What the 

 nature of the disturbing force is must be for the present a matter of theory. I am in- 

 clined to believe that it is a phase of the chemical force itself, in the same way that the 

 perturbations in the motions of the planets are a secondary result of the force of gravi- 

 tation. 



Accepting the view of the subject which has been offered, it will be obvious that the 

 very large extent of the variation in the compounds of zinc and antimony is due to the 

 very weak affinity between these elements. Were the chemical force stronger in pro- 

 portion to the disturbing force, the variation would be lessened ; were it weaker, the 

 variation would be increased. This is illustrated in the difference between the curve 

 of SbZua and that of SbZuj. It is evident from the action of chemical agents on the 

 two compounds, that one equivalent of antimony and two of zinc are united by a 

 stronger force than one equivalent of antimony and three of zinc, and we find that the 

 crystals of SbZug retain the calculated composition under a considerable variation in 

 the composition of the menstruum, whUe the composition of those of SbZna vary with 

 the slightest increase of the amount of zinc in the alloy. 



To what extent this perturbation of the law of definite proportions prevails among 

 chemical compounds, it must remain for future investigation to determine. There are, 

 however, a number of facts which tend to prove that it is very general wherever chemi- 

 cal affinity is weak. Four of these I will cite, as being remarkably analogous to the 

 facts under discussion. 



1. Riefiel, to whose investigation of the compounds of tin and copper we have al- 

 ready referred, says, after the paragraph quoted in the introduction to this memoir : — 

 " Les aiguilles de CuSn^j sent plus grosses que celles de CuSu.13. On croit, sans oser 



