EARTHS. 263 



(/.) Slacking of lime. In this familiar process, the earth com- 

 bines with about one third of its weight of water, forming a true hy- 

 drate ; and in this condition, lime kept secluded from the air, is in the 

 most useful state for the laboratory. The water may be again expel- 

 led by a red heat, contrary to the fact in the case of the hydrates of 

 potassa and soda, and of baryta and strontia. The heat, (about 800, 

 Dalton,) arises from the solidification of the water, and is much more 

 than the latent heat of the water, because ice or snow and lime slack, 

 with energy, and give out a heat of 212. Light sometimes appears, 

 when the slacking is performed in a dark place ; I have seen it from 

 the Carrara marble.* If fragments of good lime be placed in a quart 

 tumbler, filling not more than one third of it, the tumbler resting in 

 a dish, the proper quantity of water being sprinkled over it, and a tall 

 bell glass covering the whole, the vapor will rise in a dense cloud ; 

 it will soon produce currents like rain, down the sides of the bell, which 

 will become clear, as soon as it attains the boiling heat, and the steam 

 will then blow out powerfully under its sides: when the bell is lifted 

 out of the dish, the cold air will again produce a thick cloud. 



(g.) Milk or cream of lime, is the hydrate brought to the consist- 

 ence of paste with water, and thus mechanically suspended : it is 

 very useful in purifying gases from carbonic acid ; they are, for this 

 purpose, made to pass through the milk of lime, the large quantity 

 of the earth being much more effectual than lime water, which is how- 

 ever, very convenient in small experiments. 



(A.) Lime is mechanically raised in slacking, as is perceived by 

 the odor, and by the effect on test paper, placed in the steam that ri- 

 ses from it. 



(i.) Lime absorbs moisture from the air, falls to powder, and be- 

 comes a true hydrate, f 



(/.) The mere water-slacking of lime does not destroy its activity ; 

 its peculiar powers are blunted or suspended by air-slacking, the cause 

 of which will be explained under the history of the carbonate. 



4. FUSIBILITY. Extremely infusible; first partially melted by 

 Dr. Hare's compound blowpipe, in Philadelphia, and in 1812 more 

 perfectly, in the laboratory of Yale College. J The lime must be 

 shaped into the form of an acute cone, not over the size of a large 

 pin, and the focus of heat must be directed upon the apex ; when it 

 softens, subsides, and is soon covered with a vitreous glaze. Fusible 

 also in the galvanic current. The light emitted by lime, in the focus 

 of heat, is most intense ; it has been used with a stream of oxygen gas, 



* Jn a dark cellar, in JMr. Acoum's house, in London, some lime of Carrara mar- 

 ble, during its slacking, showed luminous points of mild white light. 

 1 It also absorbs carbonic acid, and loses its causticity. 

 t Afterwards by Sir H. Davy, by Galvanism. 



