262 <A New Instrument for estimating the quantity of 
Arr. IV.—A New Instrument for estimating the quantity of 
Carbonate of Lime present in Calcarecus Substances ; by J. 
Lawrence Smiru, M. D. 
Amone the most ready methods used for the purpose of esti- 
mating the quantity of carbonate of lime contained in calcareous 
substances, are Davy’s pneumatic and Rogers’ methods, the one 
estimating it from the bulk of carbonic acid, and the other by 
the weight of the carbonic acid afforded by the action of an acid. 
The principal objection to the former, is the complication of the 
apparatus, and for the latter it is necessary to be furnished with 
a more than ordinary pair of balances, and a set Fig. 1. 
of accurate weights, whereas the instrument about 
to be described is free from both these objections, 
with the additional advantage of affording more 
accurate results. 
Jt appeared at first, that by taking a certain quan- 
tity of the substance to be examined, and letting 
fall upon it by degrees a solution of acid, the 
strength of which we know, that it might be pos- 
sible to estimate the quantity of carbonate of lime 
in the same manner as the carbonates of the fixed 
alkalies are estimated; but for this to succeed, it 
is necessary that the substance should be finely 
pulverized, and free from any materials soluble in 
the acid used, but as it is not common to be fur- 
nished with these two conditions, another method 
had to be adopted, the principle of which is, to 
treat the calcareous substance with an excess of 
acid, the strength of which is known, and then to 
find out the amount of this excess, thereby know- 
ing the quantity of acid taken up, from which we 
can easily calculate the quantity of carbonate of 
lime present. In the application of this principle, 
it will be found that any thing like difficult mani- 
pulation is avoided, and that there is no calculation 
required. 
