uel 
.300 )©60- Dr. WITHERIN e's’ Experiments and Obfervations 
_ fixed alkalies, both mild and cauftic, feparated the terra ponderofa 
from marine acid, I was at a lofs to know why. Profeflor Berc-_ 
_MAWN, in: his admirable ‘table of fimple elective attractions, 
placed the terra ponderofa cauftica immediately. under the; vi- 
triolic, nitrous, and marine acids, and confequently above the 
cauftic alkalies. I. was interefted in the reality of the faéts, 
becaufe I had fo feldom feen reafon to doubt. the obfervations of 
that very excellent chemift, and: therefore made the i 
experiments. pig gf en 
To different portions of terra ponderofa Gilitat wae terra pon- 
-derofa nitrata I added, drep by drop, cauttic vegetable, cautftic 
“ foftil, and cauftic volatile alkalies. In every cafe the EARTH 
- was thrown down; and I have fo often repeated thefe, experi- 
_ments to fatisfy, myfelf and others, that Iam perfuaded the 
terra ponderota cauftica ought to be placed below the alkalies, 
except in the column appropriated to the vitriolic acid ; and-at 
may be feparated even from that acid, by the vegetable, fixed 
alkaly, if the alkaly be sent via feed | as will IPRs 1D the 
next fection. 4p 
athly, The neceffity for uf ing pure acids upon. many. ocea~ 
“ions, and the difficulty of obtaining them pure, are fufficicntly 
obvious. The virrroLic AcrD, as made i in the Jarge way, .19 
generally pure enough for moft purpofes. It is apt to,get co- 
loured by inflammable matter; but this 1s feldom an _aneonve- 
nience ;, and, when it would be-fo, it 1s ealy to drive it off: by 
boiling the acid in a Florence flafk over a common fire, But 
there is another caufe of impurity in this acid, which appears 
upon diluting it with water; for then it becomes milky, and 
in a fhort time a powder fubfides * | ee 
* About two years ago F examined this powdery matter; both that which was ~ 
thrown — 

