Modifying the force of Chemical Attractioii. 239 



"Berthollet has asserted, indeed, that a large quantity of 

 potassa, is capable of separating a small quantity of sulphur- 

 ic acid from the sulphate of barytes ; but his experiments 

 were made in contact with the atmosphere in which carbon- 

 ic acid is always flying about; but it is well known that the 

 carbonate of potassa and sulphate of baryta, mutually decom- 

 pose each other."* — Davy'^s Elements of Chemical Philoso- 

 phy. 



It appears therefore, that " the sources of fallacy" did not 

 " escape the observation of Berthollet," and that he suppo- 

 sed himself to have obviated them. He knew very well 

 that carbonate of potassa and sulphate of baryta mutually 

 decompose each other and that carbonic acid is absorbed 

 by potassa, when it is boiled in contact with the atmosphere. 

 He took care therefore, to employ such potassa as " contain- 

 ed no carbonic acid," and then carried on the process in a 

 retort, which being kept constantly filled with watery vapor, 

 the contact of the atmosphere was effectually prevented. 

 Even if this had not been the case, the quantity of carbonic 

 acid that could have entered by the beak and travelled along 

 the neck of the retort to the materials, must have been in- 

 appreciable ; certainly not adequate to the production of a 

 quantity of sulphate of potassa that could be crystallized. 

 It is obvious however, that Berthollet's experiment did not 

 differ from the common process, invented by him, for procur- 

 ing pure potassa, except that the retort was filled with the 

 vapor of water instead of the vapor of alcohol. t 



* As I have no English copy of the Chemical Philosophy to refer to, I sub- 

 join so much of Van Mons' French translation, as is retranslated above. " M. 

 Berthollet a pose en fait qu'une grande quantite de potasse peut separer une 

 petite quantite d'acide sulphurique d'avee le sulfate de baryte ; mais ses expe- 

 riences furent faites en contact avec I'atmosphere dans laquelle voltige tou- 

 jours de I'acide carbonique ; ou le carbonate de potasse et le sulfate de baryte 

 se decomposent mutuellement." 



t I have sometimes suspected, that a trivial mistake of the translator of the 

 Researches into the laws of Chemical AflBnity, in writing out his copy for the 

 press, or of the corrector of the proof sheets of the first edition, has been the 

 source of these errors. In my copy, Berthollet is made to say, " The opera- 

 tion was performed in a retort, and consequently in communication with the 

 air;" and with this the quotation of Dr. Murray, (Chemistry, Vol. I. p. 81,) 

 agrees. Berthollet, instead of any such confession, says in fact, " L'operation 

 s'est faite dans une cornue et par consequent sans le contact de I'air." The 

 conditions of Berthollet's experiment, were such as should have suggested the 

 appropriate correction. That lesser men should commit such blunders as this, 

 must evidently be, if the case be as I have supposed, it is quite natural : but 

 that Sir Humphrey Davy should build an argument, to overturn the theory of 



