1826.] On the Reciprocal Decompositim of Bodies. 279 



author of the paper. On the Poison of the Toad, lately read before 

 the Royal Society (seeAruials vj Philosophy, iorVeh.^. 137.) Dr. 

 Davy has been absent from England, on professional duty, for 

 some years, and is still abroad, we believe at Malta ; and it is 

 not extraordinary that, so circumstanced, he should not have had 

 access either to Dr. Paris's work, or to any other in which Pelle- 

 tier's experiments on the poison of the toad are recorded. — 

 C. and P.] 



Article X. 

 On the Reciprocal Decomposition of Bodies. By M. Gay-Lussac* 



We are indebted to Berthollet for the important law that 

 bodies having analogous properties mutually displace each other 

 from their combinations, and that the principal causes which 

 Hmit their separation are volatihty and insolubility. Berthollet 

 has not, perhaps, sufficiently developed the consequences of this 

 law ;^ but it is easy to predict them in every particular case. 



When two acids act on a base, and the whole remains in sola 

 lion, the base is divided between them, not according to thei*- 

 ponderable quantity, but to the number of their atoms ; and i 

 appears that its affinity for each acid has generally an important 

 share in the phaenomenon. In order to the division of the base, 

 it is enough that the acids, whatever may be their difference in 

 respect to volatility or solubihty, remain in solution; for in that 

 case they must behave as if they possessed those two properties 

 in an equal degree. 



Suppose, for instance, that we pour an excess of nitric acid on 

 chloride of sodium, the mixture will immediately contain hydro- 

 chloric acid and chlorine, and if it be heated, the chloride will 

 soon be converted into nitrate of soda. In making the converse 

 of this experiment ; that is, in treating nitrate of soda with an 

 excess of hydrochloric acid, we shall convert it into chloride of 

 sodium. These reciprocal decompositions are very easy, and 

 by converting two nitrates into chlorides, we can determine the 

 proportion in which they were mixed ; all that is necessary is to 

 know the weights of the two nitrates and the two chlorides, and 

 the atomic weight of each salt. All the chlorides are not decom- 

 posed by nitric acid with the same facility ; chloride of silver, 

 which is completely insoluble in water and acids, is not at all 

 attacked by it ; and chloride of lime is not so readily attacked 

 as the chloride of potassium or sodium. But we must also 

 observe, that we are now comparing compounds (chlorides and 

 nitrates) which are not at all analogous, and that we can only 



• From the Annalcs de Cliimie. 



