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470 Mr. Henry on the Natural Hiftory , &c. 
the nitrous and concentrated marine acids, he 
acknowledges, they difTolved entirely.* 
Mr. Kirwan, alfo fays,that this earth, per- 
fe&ly dry and free from fixed air, could not be 
difTolved in any of the acids without heat. But 
that in a heat of 180°. thefe acids, diluted with 
four or fix times their quantity of water, at¬ 
tacked it very fenfibly. There is no doubt but 
Calcined Magnefia difiolves much lefs rapidly 
than the mild. The aerial acid, contained in 
the latter, while it is expelling, keeps up, as 
Bergman has juftly obferved, an intefiine motion, 
•whereby the particles of the earth are agitated 
and feparated, fo that freih furfaces are con¬ 
tinually prefented to the Magnefia. Whereas, 
if an acid be added to this earth, when diverted 
of air, this motion is wanting, and that part 
of the acid, which becomes faturated with the 
earth, envellopes the remaining earth, and' pre¬ 
vents the immediate adion of the free acid on 
it.j; Continual agitation, however, will greatly 
promote the folution. 
Mr. Monch, feems not to have £een aware 
of the greater quantity of acid, requifite to 
diflolve Calcined -Magnefia, than would be 
neceffary for the uncalcined. Nor indeed to 
* Vide London Medical Journal, vol. III. p. 97. 
f Philofophical Tranfaftions, vol. LXXIJ. p. 193. 
I Bergman Opulc. de Magnefia. § XIX. 
have 
