116 M. Gay-Lussac on the Reciprocal Decomposition of Bodies. 



Art. XXV. — On the Reciprocal Decomposition of Bodies. 

 By M. Gay-Lussac* 



We are indebted to Berthollet for the important law, that 

 substances whose properties are analogous eventually displace 

 one another from their combinations, and that the principal 

 causes which limit the separation are volatility and insolubi- 

 lity. Berthollet did not perhaps develope the consequences 

 of this law sufficiently ; but it is easy to foresee them in each 

 particular case. 



When two acids act on the same base, and the whole re- 

 mains in solution, the base is divided between them, not ac- 

 cording to their ponderable quantity, but to the number of 

 their atoms, and it does not appear that its affinity for each 

 acid has much influence over the phenomenon. It is suffi- 

 cient, in order that the base should be divided between them, 

 that the acids, whatever may be the difference in their volati- 

 lity or solubility, should remain in solution \ for, in that case, 

 they ought to act as if they possessed those properties in the 

 same degree. 



Conceive, for example, that an excess of nitric acid is ad- 

 ded to the chloruret of sodium ; there will be both hydro- 

 chloric acid and chlorine in the mixture, and, on the applica- 

 tion of heat, the chloruret will be soon changed into nitrate 

 of soda. On reversing the experiment, that is, in treating ni- 

 trate of soda by an excess of muriatic acid, it will be convert- 

 ed into chloride of sodium. These reciprocal decompositions 

 are very easy, and, by converting two nitrates into chlorurets, 

 Ave may determine the proportion in which they were mixed : 

 all that is necessary is to know the weight of the two nitrates, 

 and the two chlorurets, and the atomic weight of each salt. 

 All chlorurets are not decomposed by nitric acid with the 

 same facility ; that of silver, which is completely insoluble in 

 water and acids, is not attacked by it, and that of calcium is 

 acted on with more difficulty than those of potassium or sodium. 

 But it must also be remarked, that we compare at present 



• Translated from the Annaks dc Chimie el dc Phg.iii/uc, vol. xxx- 



