108 
COMMERCIAL HYDROCHLORIC ACID. 
in less than a minute, the purity of the hydrochloric acid of 
commerce. According to Girardin, T ^ th part of sulphurous 
acid cannot escape detection when these means are em- 
ployed. 
Means of ascertaining, in a direct manner, the proportion 
of hydrochloric acid in an acid liquid, the specific gra- 
vity of which is unknown. 
This is made known by discovering what quantity of mar- 
ble this acid will saturate. For this purpose, take a certain 
quantity, by weight, of acid, which you dilute with two or 
three times its weight of distilled water; then drop into it a 
piece of marble, the weight of which you have previously 
ascertained. The saturation being effected, take away the 
piece of marble, wash it, and, when dried, weigh it; the differ- 
ence between the weights gives you the quantity of marble 
dissolved. To find the corresponding proportion of hydro- 
chloric acid which has been saturated, you must bear in mind 
♦ hat two atoms of hydrochloric acid, weighing 455.13, are 
exactly saturated by one atom of carbonate of lime, weighing 
632.46. 
Or in establishing a rule of three direct, you easily attain 
the fourth term of the proportion, which is the quantity 
of acid that has been saturated by the weight of marble dis- 
solved. 
Suppose that in a preliminary trial, twenty grammes of hy- 
drochloric acid had dissolved 8.45 of marble, you would have 
the following proportion: 
632.46 : 455.13 :: 8.45 : x 
x=8.45-f455.13 
-=6.08 
632.46. 
The quantities of real acid contained in solutions varying 
in specific gravity, may be estimated by reference to a table 
of Edmund Davy, to be found in Turner's Chemistry. 
