336 EXPERIMENTS ON THE METALS FROM THE FIXED ALKALIS. 



distant analogies, or upon experiments in which agents, 

 ■which they did not suspect, were concerned. No person, 

 I believe, has attempted to show, that, when potassium 

 or sodium is burnt in oxigen gas, water is formed; or that 

 water is generated, when potassium decomposes any of 

 the acids*: and no one has been able to form potassium, 

 by combiniug hidrogen with potash. I stated in the Bake- 

 rian lecture for 1807, that, when potassium and sodium 

 were burnt in oxigen gas, the pure alkalis were formed in 

 a state of extreme dryuess; and that 100 parts of potassium 

 absorb about 18 parts of oxigen, and 100 parts of soda 

 about 34 parts. Though, in the experiments from which 

 these deductions were made, very small quantities only of 

 the materials were employed, yet still, from frequent 

 ' repetitions of the process, I hoped that they would ap- 

 proach to accuracy ; and I am happy to find, thaf this is 

 the case; for the results differ very little in some experi- 

 ments, which I have made, upon considerable portions 

 of potassium and sodium, procured by chemical decompo- 

 sition. 

 Ox'gencon- When potassium is burnt in trays of platina, in oxigen 



sumed propor- g as t }j at h as been dried bv ignited potash, the absorption of 



tionaltothe 5 . . , A ,, * u- , • w • r.i 



quantity of oxigen is about ^ of a cubical inch for every gram of the 

 metal. 



Decomposition * When, in October 1807, I obtained a dark coloured combusti- 

 of boracic acid, ble substance from boracic, acid, at the negative pole in the voltaic 

 circuit, I concluded, that the acid was probably decomposed, ac- 

 cording to the common law of electrical decomposition. In March 

 1808 I made farther experiments on this substance, and ascertained, 

 that it produced acid matter by combustion ; and I announced the 

 decomposition in a public lecture delivered in the Royal Institution 

 March 12. Soon after I heated a small quantity of potassium in 

 contact with dry boracic acid, no water was given off in the ope- 

 ration, and I obtained the same substance, as I had procured by 

 electricity. Messrs Gay-Lussac and Thenard have likewise ope- 

 rated upon boracic acid by potassium, and they conclude, that they 

 have decomposed it ; but this does not follow from their theory, 

 unless they prove, that water is given off in the operation, or com- 

 bined with the borate of potash ; the legitimate conclusion to be 

 drawn from the processes, on their hypothesis, was, that they had 

 made hydruret of boracic acid. 



metal 



