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VI. Some Experiments and Observations on a new Substance which 
becomes a violet coloured Gas by Heat. By Sir Humphry 
Davy, Knt. LL. D. F. R. S. 
Read January so, 1814. 
A NEW and a very curious substance has recently occupied 
the attention of chemists at Paris. 
This substance was accidentally discovered about two years 
ago by M. Courtois, a manufacturer of saltpetre at Paris. In 
his processes for procuring soda from the ashes of sea weeds, 
(cendres de vareck) he found the metallic vessels much cor- 
roded ; and in searching for the cause of this effect, he made 
the discovery. The substance is procured from the ashes, after 
the extraction of the carbonate of soda, with great facility, and 
merely by the action of sulphuric acid: — when the acid is 
concentrated, so as to produce much heat, the substance ap- 
pears as a vapour of a beautiful violet colour, which condenses 
in crystals having the colour and the lustre of plumbago. 
M. CouRTois soon after he had discovered it, gave speci- 
mens of it to M. M. Desormes and Clement for chemical 
examination ; and those gentlemen read a short memoir upon 
it, at a meeting of the Imperial Institute of France, on Nov. 29th. 
In this memoir, these able chemists have described its principal 
properties ; they mentioned that its specific gravity was about 
four times that of water, that it becomes a violet coloured gas 
at a temperature below that of boiling water, that it combines 
