EARTHS. 267 



vegetable fibres, and thus rendering them soluble ; even tanner's bark 

 is decomposed by lime, and rendered useful as a manure ; it is thought 

 to be injurious with animal manures, unless they are too rich, and 

 need to be in part decomposed.* 



SEC. II. BARYTA. 



Name from the Greek /3apu, heavy. f 



1. DISCOVERY. By Scheele, in Sweden, in 1774; formerly 

 confounded with lime. 



2. PROCESS. 



(a.) Native, or artificial carbonate, in powder, mixed with lamp- 

 black and oil, in a ball, is strongly calcined in a crucible, for one 

 hour, by the heat of a forge or wind furnace, and the carbonic acid 

 is thus decomposed, or expelled. Boiling water dissolves out the 

 caustic earth. The theory of the process will be rendered more in- 

 telligible hereafter. 



(b.) By calcination of the nitrate of Barytes ; see that salt. 



3. PROPERTIES. 



(a.) Color, gray before slacking; consistency, porous ; after slack- 

 ing, a white powder ; sp. gr. 4. 



(b.) Taste acrid and caustic ; poisonous. 



(c.) Affects the test colors, as lime and the alkalies do. 



(d.) The hydrate is fusible in its own water, of which it contains 

 about 9 or 10 per cent. 



(e.) Baryta, even when obtained from the nitrate, is fusible by the 

 compound blowpipe.f 



(f.) Water causes it to slack with much greater energy than 

 lime ; the phenomena and theory are the same, but much more strik- 

 ing, and light is said to be sometimes emitted. The water slacked 

 baryta, is a true hydrate, and as the earth is represented by 78, and 

 there is one proportion of water in the hydrate, the equivalent num- 

 ber is of course 87. 



It slacks in the air, as lime does, and for the same reason. 

 It dissolves readily in 20 parts of water at 60, and if boil- 

 ing, in 2 parts. 



(i.) On cooling, it forms regular crystals flattened hexagonal 

 prisms. 



*a 13 vi 



if:} 



* See Davy's Agricultural Chemistry, and Ure's Diet. 



t The natural sulphate is known to the miners, by the name of heavy spar. 



t Respectable authors state that baryta thus prepared is infusible, but they 

 had probably not tried the compound blow-pipe. 



The observation is attributed to Dobereiner, and it will not appear very extraor- 

 dinary, since lime sometimes exhibits light while slacking, although the energy of 

 the action is much less remarkable. 



