Scientific Intelligence.— 'Chemistry. 219 



menced with it. M. Gay-Lussac, therefore, considers it as proved, 

 thattheinfluenceof aqueous vapour, in the calcination of limestone, 

 is confined to the production of a vacuum for carbonic acid, and 

 to the prevention of the pressure of the disengaged acid, upon 

 that which remains with the lime. When the vapour is present, 

 a lower temperature is required to dislodge the carbonic acid ; 

 but the importance of this influence must not be overrated. 

 The water, in calcareous stones, is mechanically interposed be- 

 tween their particles ; and, with the exception of some minute 

 portions, which remain confined in the centre of pieces too large 

 to allow of the heat penetrating and vaporizing them, the greater 

 part of the water must evaporate without any useful result ; 

 and, on the contrary, with the loss of fuel, before the limestone 

 has acquired the temperature requisite for its decomposition. 

 M. Gay-Lussac thus concludes : — " I am certainly convinced 

 that the vapour of water favours the calcination of limestone, 

 but I am doubtful as to its possessing real advantages, because 

 there is not a great difference in the temperature at which it de- 

 composes alone or with the vapour of water ; besides, if the va- 

 pour of water only exerts a mechanical action similar to that of 

 atmospheric air, any important advantage which it possesses over 

 the aeriform current continually passing over the burning mass, 

 is not evident. The readier decomposition of carbonate of lime 

 by the access of aqueous vapour, or rather by means of a va- 

 cuum, cannot be considered as an isolated fact. It may be re- 

 garded as an estabHshed principle, that when one or several 

 gaseous products are obtained, either by the action of heat or a 

 chemical agent, the decomposition may be generally facilitated 

 by keeping the bodies in vacuo, or by preventing the gaseous 

 fluids from pressing upon it. And on the other hand, the de- 

 composition may be retarded or entirely prevented, by forming 

 round the body a sufficient pressure of an elastic fluid of the 

 same nature as that which is to be disengaged. It is thus in 

 the curious experiment of Sir James Hall ; carbonate of lime 

 was fused at a very high temperature, without being decom- 

 posed, under the influence of a sufficient pressure of carbonic 

 acid. — Ajin. de Ch. et de Ph. Ixlii. 219- 



