Therefore, in the mixture under consideration, X and Y are both said to
be at a "partial pressure" of half an atmosphere, which is manifestly 7.5
lb. per square inch. Clearly, when a gas is an entity (either an element
or one single chemical compound) partial and total pressure are
identical. Now, it has been shown that acetylene ceases to be a safe gas
to handle when it is stored at a pressure of 2 atmospheres; but the limit
of safety really occurs when the gas is stored at a _partial_
pressure of 2 atmospheres. Neat acetylene, accordingly, cannot be
compressed above the mark 30 lb. shown on a pressure gauge; but diluted
acetylene (if the diluent is suitable) may be compressed in safety till
the partial pressure of the acetylene itself reaches 2 atmospheres. For
instance, a mixture of equal volumes of X and Y (X being acetylene)
contains X at a partial pressure of half the total pressure, and may
therefore be compressed to (2 / 1/2 =) 4 atmospheres before X reaches the
partial pressure of 2 atmospheres; and therewith the mixture is brought
just to the limit of safety, any effect of Y one way or the other being
neglected. Similarly, a mixture of 1 volume of acetylene with 4 volumes
of Y may be safely compressed to a pressure of (2 / 1/5 =) 10
atmospheres, or, broadly, a mixture in which the percentage of acetylene
is _x_ may be safely compressed to a pressure not exceeding (2 /
_x_/100) atmospheres.
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