1823.] Scientific Intelligen&R. 



and commodious for practice), it occurred to me, that one part of the 

 apparatus made use of, might, with advantage, be still further simpli- 

 fied ; and as every circumstance, however apparently obvious, Or tri- 

 vial in itself, which, in any degree, tends to facilitate the production, 

 in greater quantity, of so powerful a chemical agent as potassium, is of 

 importance, I have thought that the mode of operating which I pursued 

 might not be wholly unworthy the notice of this Society." 



** It is well known that the grand difficulty in successfully perfbrm- 

 ing the experiment in question, consists in protecting the gun-barrel 

 from the effects of that extreme and long-continued heat, which is 

 necessary to decompose the alkali, and to volatilize its base. The usual 

 practice hitherto has been to surround with a lute that portion df the 

 gun-barrel which is introduced into the fire. This operation, hdwievfer, 

 is always tedious ; and although it be conducted even with the greatest 

 care, it is found extremely difficult to prevent fissures in the coating, 

 particularly when the heat is much increased in the course of the expe- 

 riment. Hence, if eventually the fire have direct access to the barrel, 

 through any crevice which may be formed, the fusion of the denuded 

 part is generally the consequence, and the Whole labour of the e^xperi- 

 ment is lost.'* 



" This then being the common cause of failure, it occurred to iiie 

 that, if there were substituted for the luting, a thin but sound arid 

 well-burnt tube or hollow cylinder of Stourbridge clay* of such dimen- 

 sions as just to cover that portion of the barrel which is subjected to 

 the fire, the unfortunate result, which I have alluded to, might possibly 

 be avoided." 



" A tube of this description was accordingly procured ; and in order 

 to guard against the hazard of its cracking, by reason of exposure to a 

 sudden increase of temperature, it was, in the first place, gradually and 

 with caution, heated to redness." 



" The remaining part of the experiment was then performed with 

 entire success ; and a very considerable quantity of potassium ob- 

 tained.'* 



" It may be proper to remark that the hollow cylinder, and that por- 

 tion of the gun-barrel which it incloses, should be of such relative 

 diameters that, when cool, their corresponding surfaces are ndt ^uite 

 in close contact; otherwise the cylinder will be in danger of burstihgj 

 not only on account of its own contraction, but also on account of the 

 simultaneous expansion of the gun-barrel, from the effects of that very 

 high temperature, to which, in this state of combination, they are sub- 

 mitted." 



" Moreover, the whole apparatus should be supported accurately in 

 the same position throughout the experiment (by means of rests made 

 of Stourbridge clay), and should be so situate in the fire, that the ma- 

 terials operated upon may, during the whole process, be submitted to 

 its greatest intensity." 



" With due attention to these precautions, and to some minor cir- 

 cumstances in the manipulation of the experiment, which I shall not 

 take up the Society's time in detailing, it is believed that the decompo- 

 sition of potash, by means of iron, might, in every instance, be effected 

 with almost entire certainty, and potassium be obtained in great abun- 

 dance."— (Cambridge Phil. Trans. 1822. Part II.) 



