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PHYSICAL anp LITERARY. 229 
thods of obtaining it in its pure ftate, and 
free of fixed air. The firft of thefe is the 
feparation of the alkali from an acid, 
merely by heat; an inftance of which we 
have from Mr Margraaf*. He prepared 
from urine an ammoniacal falt, the acid 
of which is the bafis of the phofphorus, 
and is of fuch a peculiar nature, that it en- 
dures a red heat without being diflipated« 
Sixteen ounces of the neutral falt were 
fubjected by him to diftillation. The a- 
cid remained in the retort, and he foundin 
the receiver eight ounces of an alkaline 
fpirit, which, he tells us, was extremely vo- 
Jatile, very much refembling the fpirit of 
falt ammoniac diftilled with quick-lime ; 
-and no cryftals were formed,in it, when 
expofed to the cold air. 
A cauftie volatile alkali may alfa be. 
obtained, by mixing falt ammoniac with 
half its weight of a cauftic fixed alkali, or 
of magnefia which has been previoutly de- 
prived of its air by fire; and then fub- 
mitting thefe mixtures to diftillation : Or, 
merely 
a * Mem. de !’Acad. de Berlin, an. 1746, p. 87+ 
