178 Miscellaneous Jntelligence. 



precipitated by subcarbonate of potash, heated, and filtered 

 whilst hot, gave 24.75 parts ; another 100 parts, precipitated, 

 heated, and then allowed to stand for 24 hours, gave only 

 18.845 parts ; and a third 100 parts, precipitated without heat, 

 gave but 13.9 parts. 



Caustic potash precipitates magnesia perfectly, either with or 

 without heat. 



Objections are taken to the method of separating lime and 

 magnesia, by first converting them into sulphates ; first, be- 

 cause of the great difficulty of driving off the water- from the 

 sulphate of magnesia; second, because of the difficult solu- 

 bility of heated and dry sulphate of magnesia in water ; and 

 third, because of the decomposition in part of the sulphate of 

 magnesia by long and high heats. A heat of 260°, (centigrade?) 

 for five hours, dissipated only about f of its water. A white 

 heat for three quarters of an hour did not drive off the whole. 

 Heated for three quarters of an hour to whiteness, it began to 

 lose acid, and was not again perfectly soluble. When heated, 

 it is diflfiicultly soluble in water ; it requires eight or ten times the 

 quantity of water required for the common sulphate of mag- 

 nesia, and to be left many hours in contact with it ; and this 

 effect is produced by a heat by no means extraordinarily high. 

 Some that was dried in phials, in a sand bath, was as tardy 

 in dissolving as that which had been dried at a white heat. 



The conclusions contained in the paper are — 1. That the sub- 

 carbonate of ammonia is the best agent to separate lime from 

 magnesia. 2. That fixed alkaline subcarbonates, though 

 heated, precipitate magnesia imperfectly. 3. That carbonate 

 of magnesia is soluble in alkaline salts. 4. That caustic potash 

 precipitates magnesia perfectly ; and that it, or caustic soda, 

 should always be used for the precipitation in analysis, 5. 

 That sulphate of magnesia, long calcined, even at low heat, is 

 difficultly soluble in water. 6. That magnesia, heated to white- 

 ness, retains 20.78 per cent, of water. 



The following tables express the composition of certain mag- 

 nesian compounds. 



