For determining the alkalimetric strength of commercial sodas, a known
weight of the sample is dissolved in water, and a few drops of a
solution of methyl orange are added, which colour the solution yellow or
orange. Into this solution is then run, from a burette or graduated
tube, a standard solution of an acid, that is, a solution prepared by
dissolving a known weight of an acid, say hydrochloric acid, in a known
volume of water. The acid is run in gradually until the yellow colour
changes to pink, at which point the volume of acid used is noted.
Knowing the weight of acid contained in this volume of standard acid,
and having regard to the law of equivalence mentioned above, it is an
easy matter to calculate the amount of alkali equivalent to the acid
used, and from this the alkali contained in the sample.
_Sulphuric Acid._--The first process for manufacturing sulphuric acid or
vitriol was by placing some burning sulphur in a closed vessel
containing some water. The water absorbed the acid formed by the burning
sulphur.
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