on various Objects, *15 



which agent, which they did not suspect were concerned. 

 No person, I believe^ has attempted lo show that when 

 potassium or sodium is burnt in oxygen gas, water is form- 

 ed, or that water is generated when potassium decomposes 

 any oi the acids *j and no one has been able td form potas- 

 sium, by combining hydrogen with potash. I stated itt 

 the Bakerian lecture for 1807, that when potassium and 

 sodium were burnt in oxygen gas, the pure dkaVies wqtg 

 formed in a state of» extreme dryness; and that 100 parts 

 of potassium absorb about 18 parts of oxygen, and iOO 

 parts of soda about 34 parts. Though, in the experiments 

 from which these deductions were made, very small quan- 

 tities only of the materials were employed ; yet still, from 

 frequent repetitions of the process, I hoped that they would 

 approach to accuracy ; and I am happy to find that this 

 is the case; for the results differ very little in some ex* 

 periments which I have made upon c msiderable portions 

 of potassium and sodium, procured by chemical decom- 

 position. 



When potassium is burnt in trays of platina, in oxygen 

 gas that has been dried by ignited potash, the absorption 

 of oxygen is about i^ of a cubical inch for every grain of 

 the metal consumed ; and when sodiuiii is burnt in a si- 

 milar manner, about a cubical inch is taken up for every 

 grain f. The alkalies so formed, are only imperfectly fu- 

 sible at a red heat; and do not, like the easily fusible alka- 

 lies, give indications of the presence of moisture. 



M. D'Arcet has shown by some very well conducted 

 inquiries, that potash and soda J, in tlicir common state, 

 contain a considerable proportion of water; and M. Ber- 



* When in October 1807, I obtained a dark-coloured combustible sub- 

 stance from boracic acid, at the ii'eg-ative pole m the Voltaic circuit, I con- 

 cluded that tlie acid was probably decomposed, according to the common 

 law of electrical decomposition, lnMar:li 1308. I made turther experi- 

 ments on this substance, and ascertained thai it produced acid matter by- 

 combustion; and I announced the decomposition in a public lecture de- 

 livered 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 operation, and I obtnined the same substance as I had procured 

 by electricity. MM. Gay Lussac and Thenard have likewise operated upon 

 boracic acid, by potassium, and they conclude that they have decompounded 

 it; but this does not follow from their theory, unless they prove that water 

 is given off in the operation, or combined with the borate of potash: the 

 legitimate conclusion to be drawn from the processes, on their hypothesis, 

 was, that they had made a hydruret of boracic. acid. 



f The quantities of gas given out by the operation of water, are in a si- 

 milar ratio. See page 43 of the last Bakerian lecture [PhiJ. Mag. vol. xxxiii. 

 p. 432,] and page 26 of this paper [p. 407 and 408 preceding.] 

 I Aanales de Chimie, Nov. 1808, page l75. 



thollet 



