dangerous
mixture, that the more common solution is one in which methylene iodide
is saturated with a mixture of iodoform until it shows a specific
gravity of 3-601 ; and by using the methylene iodide alone, in its pure
state, it having a specific gravity of 3'2981, the stones to that
weight can be isolated, and by diluting this with benzole, its weight
can be brought down to that of the benzole itself, as in the case of
Sonstadt's solution. This solution, in full standard strength, has a
specific gravity of 3.1789, but may be weakened by the addition of
distilled water iu varying proportions till the weight becomes almost
that of water.
Knowing
the specific gravity of all stones, and dividing them into six groups,
by taking a series of standard solutions selected from one or other of
the above, and of known specific gravity, we can judge with accuracy if
any stone is what it is supposed to be, and classify it correctly by
its mere floating or sinking when placed in these liquids. Beginning
then with the pure double nitrate of silver and thallium, this will
isolate the stones of less specific gravity than 4- 7963, and taking
the lighter solutions and standardising them, we may get seven
solutions which will isolate the stones as follows :—
