on the Terra Ponderofa, der i | ue 299 
— 
is the want of water which prevents the fixed air iinittabigns its 
élaftic aérial ftate ?’ This fuppofition becomes ftill more proba- 
ble, if we obferve that ‘when the folution of the fpar in an 
acid is precipitated by a mild alkaly, C. 1. 2. fome water en- 
“ters into the compofition of the precipitate, for it weighs the 
fame as before it was diffolved, and yet contains only 20 ounce 
“meafures of fixed air, whilft the native {par contained 25 ounce 
ameafutes ; ; fo that there is an addition of weight equal to that 
of 5 ounce meafures of fixable air, or 33 grains to be accounted 
for, Which can’ only arife from the water; and this precipitate, 
‘thus united to’ Sala RE Sahel lofes its ee acid in the os. 
Ei I. BE { ous : 
‘athly, Prone? BercMawn fuppofes the terra ponderofa to 
be a metallic earth *; its entire feparation from an acid by 
‘means’ of the phlogifticated alkaly (D. 5-) certainly favours 
~~ fuch a fappofition ; but, if it’be fo, it is evident from experi- 
“ments H. Ly 2. that: other means than thofe commonly em- 
, ployed muft be ufed to effet its reduétion.. 
sthly, The precipitate made by the cauftic vegetable alk ty 
D. 4. taking fome of the alkaly down with it, and thus form- 
ing a fubftance’neither foluble in ‘water nor in acids, 1s a very 
curious phenomenon.» : 
‘Tafterwards varied the experiment by adding the terra’ pon- 
derofa lime-water (E.) to cauftic vegetable and cauftic: foffil 
‘alkaly. In both cafes this infoluble’ compound was itnme- 
diately formed; but not fo when cauftic volatile alkaly was ufed. 
This comipofition of an alkaly and an earth certainly deferves 
“more attention than Iam at prefent able to beftow. upon it. 
é6thly, As it appears from ‘experiments D. 1.2. 3. 4. that 
..* See preface to his Sciagraphia Regni Mineralis. 
RR i2 ; fixed 
