266 A New Instrument for estimating the quantity, §§c. 
around where the ammonia falls, is thrown out of solution, and 
if we stir the liquid, the alumina will be redissolved so long as 
there is any free acid, so that when the flocks of alumina are no 
longer taken up, we are furnished with an assurance that the 
process is nearly completed. The acid that the alumina and iron 
takes up is acted upon by the ammonia, with almost the same 
readiness as if free, so that no cause of error is to be apprehended 
from that source. — 
Tt may sometimes happen from oversight, that too much am- 
monia is added; notwithstanding this, the analysis need not be 
lost. Still holding the instrument in the left hand over the cup, 
having of course arrested the flow of the fluid, we pour some of 
the acid solution into the wine-glass, introduce the small end of 
the acid instrument into it, and allow it to rise on the inside to 
either of the small marks, and add this acid to the liquid and go 
on as before with the experiment, and at the conclusion read off 
what is indicated and to it add ten or twenty according as we 
‘may have added the acid measured by the first or second mark. | 
~ After what has been said, a few words will suffice to explain 
how the instrument operates. : 
It takes 50° of acid to dissolve fifty grains of carbonate of lime, 
or 1° to dissolve one grain, and it takes 2° of the ammonia solu- 
tion to neutralize one of the acid, and therefore in treating a sub- 
stance consisting in part of carbonate of lime, for every grain that 
is present one degree of the acid is taken up, so that when we 
come to add the ammonia, we know how much of the acid is 
taken up by the quantity of ammonia left behind, thereby know- 
ing the number of grains of carbonate of lime, which we multiply 
by two, (as fifty grains of the substance was used,) to arrive at 
the per centage. This multiplication is not actually performed, as 
the instrument is so graduated as to dispense with it. 
_ Were it at all necessary to give any evidence of its easy appli- 
cation, I might state that it, along with the fluid, has been placed 
in the hands of persons entirely unacquainted with chemistry; 
and even with the principle of the instrument, and they have, 
with some little instruction in the manipulations necessary, ob- 
tained results only one or two per cent. out the way, in their first 
examination, 
