386 Miscellaneous Intelligence. 



to be dissolved in a convenient quantity of water, ten pounds of the 

 colour obtained as above added to it, and the whole heated over a 

 moderate fire ; the colour will soon change and take the tint required. 

 If boiled too long, the colour approaches that of Scheele's green, but 

 always surpasses it. The alkaline liquor remaining may be used in 

 the preparation of Scheele's green. — Ann. de Chim. xxiii. 412. 



22. Peculiar Effects of burning on Limestone or Chalk. — M. Vicat, 

 of whose excellent work on Cements and Mortars we gave a short 

 account, vol. x. p. 407, has lately obtained some singular results in 

 the burning of lime. Many years since he observed, whilst burning 

 pure lime with charcoal and coal in a small furnace, that if the 

 fragments of lime on passing through the furnace into the ash-pit, 

 were again put in with fresh fuel, and this many times successively, a 

 lime was obtained incapable of slaking, but which, broken up and 

 made into a paste, had the remarkable character of setting under 

 water. 



It is an old opinion among lime-burners that limestone which has 

 cooled before it has been completely burnt, cannot by any quantity 

 of fuel be converted into quick lime, and M. Vicat considers this 

 opinion as supported by the experiment above. It appears to result, 

 M. Vicat says, that pure calcareous matter, as chalk or marble for 

 instance, may be brought by fire into an intermediate state, being 

 neither lime nor a carbonate, and that in this state it has the pro- 

 perty, when pulverised and made into a paste, of setting under water. 



Chalk converted into lime, and slaked in the usual way, yields 

 a hydrate, which, made into a paste, will not harden in water : 

 but the same lime left to fall into powder by long exposure to the 

 air, and then made into a stiff paste with water, will solidify very 

 sensibly after immersion. The action of the air here occasions the 

 formation of a compound analogous to that afforded by imperfectly 

 burnt chalk, being like that, neither completely lime or completely 

 carbonate ; and it enjoys the same hydraulic properties. 



Ten equal portions of finely-powdered chalk were taken, and a 

 plate of cast iron being heated red hot, they were placed upon it ; 

 one portion was allowed to remain three minutes, another six, a 

 third nine, and so on, and during the time they remained on the plate 

 they were continually stirred, that all parts might be equally cal- 

 cined. These portions were mixed up, with a small quantity of 

 water, into pastes of equal consistency, no signs of slaking were ob- 

 served ; the first portions gave the ordinary odour of moistened chalk, 

 the latter portions gave the alkaline odour belonging to lime, and were 

 decidedly alkaline. After twenty-four hours of immersion in water 

 all the numbers, except the first had set, as hydraulic lime would 

 have done, and became harder daily, whilst the first remained soft. 

 When, after some time, the comparative hardness of the second and 

 the tenth were tried, no apparent, difference could be perceived. 



