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XL\. A Description of the Apparatus by which, the Frmck 

 Experiment on the Decomposition of Potash has leen made 

 ■ at the Royal Institution* . 



JL his apparatus (see Plate VII.) consists of a common 

 gun -barrel curved, to which there is adapted an iron tube 

 of the Rapacity or' two cubic inches for the potash. At the 

 bottom of this tube is a very small hole, through which the 

 potash gradually flows. 



In this experiment, the iron turnings are first heated to, 

 whiteness ; the potash is then slowly fused, and flows on 

 the turnings, where it is decomposed, and its base is found 

 condensed near the other extremity of the barrel. 



The proportions from which the best results have been 

 obtained, are about 2t parts of iron turnings A to If- parts of 

 potash. 



In order to the complete success of this experiment, ,some 

 precautions are necessary. The whole of the! apparatus 

 should be perfectly dry, clean, and impervious to air ; the 

 turnings free from oxidation, and the potash very dry; which 

 last is effected by heating nearly to redness. Pure or cry- 

 stallized potash in its usual state of dryness contains a suf- 

 ficient quantity of water to occasion the failure of the expe- 

 riment. The tube containing the potash should be surround- 

 ed by ice until the turnings arc white-hot ; and that part of 

 the barrel where the potassium sublimes, should also be kept 

 cool during the whole of the process. The barrel must be 

 carefully luted. It is proper to examine the lute after it has. 

 been exposed to a red heat, in order to repair any cracks 

 which the fire may have occasioned. A tube of safety with 

 a little mercury or naphtha should be cemented to the bar- 

 rel, to prevent the communication of the external air. 



At the commencement of the decomposition, hydrogen 

 gas is evolved, and continues to come over during the whole 

 of the process. Towards the end of the experiment a very 



* For this communication, which will prove highly acceptable to many 

 of our readers, we are indebted to Mr. E. Davy, a cousin of the professor, 

 and a very promising young chemist. 



intense 



