of Muriatic Acid and Water. 75 
‘ 
the muriatic acid bears to its density, affords 
an easy method of determining the strength, 
or specific gravity, and this F imagine may 
be done with a degree of accuracy, sufficient 
at least: for all common occasions, where the 
acid is used for manufacturing purposes; and 
the simplicity of the process scarcely admit- 
ting of material error, is not the least circum- 
stance in its favour. 
No doubt the same might be done with re- 
gard to the sulphuric and nitric acids, but 
from what has been stated, it will be readily 
seen that a proper apparatus for this purpose 
will not be so easily constructed. For the 
muriatic acid the scale of graduation is ob- 
tained from a single experiment with water 
alone, the specific gravity of which is had 
without labour (except as far as regards its 
temperature. ) 
In constructing any apparatus for this pur- 
pose it is perhaps desirable to use lenses which 
are less convex than those noticed, in order 
to increase the focal distance, and thereby 
render any small uncertainty in it, of less 
importance, when compared with the whole, 
than it would be were that whole distance 
materially lessened; as it must be obvious 
that the aecuracy of which an instrument of 
this kind is susceptible, depends upon the 
