[ 225 ] 
This experiment being repeated with magnefia, 
and with the earth of alum, Ihewed no fenfible dif- 
ference. 
The quantity of iron, left difToIved in the liquor, 
was found in proportion to the volume of air ge- 
nerated during the faturation. 
If the quantity of alcali or abforbent earth was in- 
fufficient to faturate the acid, part of the iron would 
remain in the water after boiling. All which were 
difcoverable by the tincture of galls. 
Experiment VIII, 
To a pint of didilled water, being faturated with 
fixed air, and containing four grains of chalk, was 
added a grain of iron in folution j the mixture con- 
tinued pellucid. 
Another grain of dififolved iron was diluted with a 
like quantity of water, previoufly faturated with air 
from a folution of pearl-afla in vitriolic acid: eight 
grains of fait of tartar, cryftallized with fixed air, and 
diffolved, were added to this mixture : a flight de- 
gree of cloudinefs enfued, but difappeared on fliak- 
ingj after which the liquor much refembled Spa- 
water ; only it tafled flronger of the iron. The 
quantity of chalk, and alcaline fait, in this experi- 
ment, was more than fufficient to neutralize the 
acid. 
Both the above mixtures, on expofure, became 
turbid, threw up pellicles, depofited ferruginous fedi-* 
ments, and loft their power of ftriking a purple with 
galls. 
VoL. LIX. G g 
Solutions 
