ON CHEMISTRY. 
7 
by comparison, recourse must be had to the other parcel of soil of 
180 grains. The contents of the basin or flask, must be poured into 
an accurately weighted filter placed in a glass funnel, and the liquor 
or which percolates is to be caught in a glass vessel; the soil in the 
paper is to be washed repeatedly with pure water, till it drop free 
from acid flavoured, and the filter, after being laid for a time upon 
a lump of chalk, is to be dried and weighed as before: the loss of 
weight, when perfectly dry, will indicate the quantity of matters dis¬ 
solved, but not that of the carbonate of lime only, because, the solu¬ 
tion contains a certain portion of iron,—if not magnesia, &c. Ano¬ 
ther test, therefore, must be resorted to. 
4. Process by Prussiate, or ferro cyanate of Potash. —Dissolve 20 
grains of the salt in about half an ounce of water, weigh this solution, 
and drop it by degrees into that of the previous process. A copious 
precipitate of Prussian blue will be produced, and additions of the 
test are to be made till no more precipitate be formed. The process 
cannot be effected at once, because so much blue is often present, 
that the whole of the liquid is full of it, and time must be allowed to 
let it subside: try the clear fluid thus, till the falling drop of the test 
cease to yield any blue; then again pass the solution through a 
weighed filter, let it drop perfectly free from blue, and wash the pre¬ 
cipitate till no saline taste be discernible. Reserve the blue for 
another operation. 
Into the clear liquor drop strong solution of Carbonate of Potash: 
(this forms the 5th process,) and continue the addition till efferves¬ 
cence cease, and a white precipitate fall down. Solution of Carbonate 
of Potash is to be added to some excess, the acid will then be sub¬ 
dued, the chalk will be yielded, and the supernatant fluid will be 
muriate of potash, with a slight redundance of alkali. Prepare a 
filter, weigh it,—pour in the liquid and its sediment, and proceed as 
before ; that is—in this and in all other similar operations , wash the 
precipitate with clear rain water, till no taste be perceived: then ab¬ 
sorb the water left in it, placing the filter first on apiece of dry chalk, 
and then by applying heat. The weight of paper and its precipitate 
will now indicate the quantity of the latter, which ought to corres¬ 
pond, very closely with that determined by the previous calculation. 
Thus, if every process have been correctly conducted, there will be 
found about 15 grains of carbonate of lime upon the filtering paper, 
and this will agree with the estimate. 
Magnesia, perhaps to the extent of a grain or two, may exist with 
the chalk in the filter. The mode of ascertaining the fact would be 
tedious, and my limits prevent the description of it here. 
