126 Mr Haidinger on the changes xvhkh take place 



which will stop the discharge of the gas when the flame is ex- 

 tinguished without shutting the stop cock. 



My plan or invention for the above purpose is as follows : 



Immediately above an argand, or other burner, and sur- 

 rounding the bottom of the flame, I place a hoop of brass 

 lined with steel, shown at a b, Plate I. Fig. 7 and 8, and having 

 an opening on one side at b, with a small projection b, c, on 

 each side of the opening. 



The gas being ignited, the brass expands more than the 

 steel, and thereby brings together the opening of the hoop, so 

 as to grasp a piece of metal e d, connected to the cock or 

 valve at g by the levers ef^fg. 



Should the gas be extinguished, the hoop a b cools, and im- 

 mediately contracts, so as to relinquish its grasp of the piece 

 of metal d e in connection with the cock or valve g, and by 

 which the said cock or valve is held open, and consequently the 

 end doi de escapes from b c, and by its descent shuts the cock 

 g. Although the hoop above-mentioned has been made of 

 brass and steel, it may be made of any other metals that will 

 act in the same way. 



I have sent you a burner and cock fitted up with the above 

 hoop, and a connection with the cock, merely to show you 

 more clearly the principle upon which it acts. — I am. Sir, 



Your obedient servant. 

 Portable Gas Company's Office, Wm. Warden. 



2\st April 1826. 



Art. XXVII. — On the Gradual Changes 'which take place 

 in the interior of Cupriferous Minerals, while their external 

 form remains the same. * By William Haidinger, Esq. 

 F. R. S. E. Communicated by the Author. 



Mineralogists are very generally acquainted with the cry- 

 stals from Chessy in France, having the form of blue copper, 

 but consisting of fibrous masses of malachite. Such varieties 

 are found in that locality, as well as perfect homogeneous crys- 



* Extracted from a paper read before the Royal Society of Edinburgh 

 on the 16th of April 1827. 



