496 Intelligence mid Miscellaneous Articles. 



undergoing some changes, difficult to describe, it grew fainter at 

 twenty minutes before eleven. A white arch then appeared in the 

 usual situation of the Aurora, giving out white streamers at a few 

 minutes before eleven. This latter arch was not well defined. At 

 ten minutes after eleven the Aurora had almost entirely disappeared, 

 excepting a reddish patch between Arcturus and Regulus, which in 

 ten minutes more was no longer to be seen. After this the wind, 

 which during the day had been at S.W., shifted to the N.VV., with 

 a cloudless sky, and ren»ained so until the morning. The stars, 

 however, became gradually very ill defined ; and during the whole 

 of the next day and night there fell unceasing torrents of rain, with 

 a gale of wind from the south-west." 



ON THE DECOMPOSITION OF CARBONATE OF LIME BY HEAT. 



M. Gay-Lussac observes, that it has long been supposed that the 

 calcination of limestone is accelerated by the presence of water ; 

 and tlie opinion appears to be adopted by lime-burners in general. 

 M. Dumas admits the influence of water to be unquestionable, and 

 he gives two explanations of its action ; either, says he, it acts upon 

 the carbonate, and forms a temporary hydrate, taking the place of 

 the carbonic acid for a very short time, for the hydrate of lime it- 

 self is decomposed by a red heat ; or the water being decomposed 

 by the carbon, employed as a combustible, is converted into various 

 gases, of which carburetted hydrogen forms a part, and this re- 

 acting upon the carbonic acid of the carbonate tends to convert it 

 into oxide of carbon, and thus facilitates the separation from the car- 

 bonate of lime. Thus, limestone fresh quarried, and consequently 

 still moist, ought to be more readily calcined than the stone which 

 is nearly dry ; and most lime-burners are well acquainted with this 

 fact, and sprinkle with water the limestone which has been long 

 procured before they charge the kilns with it. (Dumas, Traits de 

 Chimie, ii. p. 482.) 



The first of these explanations is, however, inadmissible, for 

 hydrate of lime is decomposed at a temperature considerably lower 

 than that at which carbonate of lime is decomposed under the in- 

 fluence of water. 



On considering the circumstances of the combustion in limekilns, 

 the second explanation does not appear to M. Gay-Lussac to be ap- 

 plicable, and he therefore proceeds to some observations which he 

 thinks will explain the influence of the water. 



A porcelain tube was filled with bits of marble and placed in a 

 furnace, the heat of which was easily regulated ; a glass retort con- 

 taining water was adapted to one end of the tube, and at the other 

 end a glass tube to receive the carbonic acid gas. The heat was 

 raised sufficiently high to decompose the marble, and on shutting the 

 ash. pit door the heat fell to a dull red, and the carbonic acid ceased 

 to come over ; and at this instant the water was boiled in the re- 

 tort, and carbonic acid was abundantly obtained. On disconti- 

 nuing the vapour, the disengagement of acid instantly ceased, and 

 returned only on continuing the vapour. 



