e« the fpecific Gravities, &C. of Saline Subfiances. 1 93 
OF MAGNESIA OR MURIATIC EARTH. 
This earth, perfectly dry and free from fixed air, eould not 
be diffolved iri any of the acids without heat. In the tem- 
perature of the atmofphere even the flrongefl nitrous acid did 
not act upon it in twenty- foil r hours; belt in a heat of i8o° 
thefe acids diluted with four or fix times their quantity of 
water attacked it very fenfibly ; but as much of the acids is 
diflipated by heat* I could not judge of the exabl quantity of 
acid requifite to diflblve a given quantity of it, any others 
wife than by precipitating the folutions by another fiibftance* 
whofe capacity for taking up acids was known. The fub- 
fiance I ufed was a tolerably cauftie vegetable alkali; By this 
method I found, that ioo gr. of pure magnefia take up 125 gr. 
of mere vitriolic acid, 132 of the nitrous, and 140 of the 
marine. None of thefe folutions reddened vegetable blues ; 
all of then! appeared to contain fomething gelatinous ; that in 
the marine acid became gfeenifh 011 {landing fo'r fome time. 
1 00 gr. of perfectly dry Epfom fait contain 45,67 of mere 
vitriolic acid, 36,-54 of pure earth, and 1 7,83 of water ; but 
100 gr. of cryflallized Epfom lofe 48 by drying, and con fe- 
quently contain 23,75 of acid, 19 of earth, and 57,25 of 
water. Common Epfom fait contains art excefs of acid,- fol- 
ks folutiort reddens vegetable blues. 
100 gr. of nitrous Epfom, well dried, contain 35,64 of 
acid, 27 of pure earth, and 37,36 of water. 
The folufion of marine Epfom cannot be tolerably dried 
Without lofing much of its acid, together with the water. 
The fpecific gravity of pure muriatic earth is 2,3296. 
Vol. LXX 1 I, C c OF 
