till tub, is affected by it. To shew the action of
this test, the following experiments will serve.

EXPERIMENT.

Pour into a wine-glass containing distilled water, an equal quantity of
water impregnated with sulphuretted hydrogen gas: no change will take
place; but if a 1/4 of a grain of acetate of lead (sugar of lead of
commerce), or any other preparation of lead, be added, the mixture will
instantly turn brown and dark-coloured.

To apply this test, one part of the suspected water need merely to be
mingled with a like quantity of water impregnated with sulphuretted
hydrogen. Or better, a larger quantity, a gallon for example, of the
water may be concentrated by evaporation to about half a pint, and then
submitted to the action of the test.

Another and more efficient mode of applying this test, is, to pass a
current of sulphuretted hydrogen gas through the suspected water in the
following manner.

EXPERIMENT.

[Illustration]

Take a bottle (_a_) or Florence flask, adapt to the mouth of it a cork
furnished with a glass tube (_b_), bent at right angles; let one leg of
the tube be immersed in the vial (_c_) containing the water to be
examined; as shewn in the following sketch. Then take one part of
sulphuret of antimony of commerce, break it into pieces of half the size
of split pease, put it into the flask, and pour upon it four parts of
common concentrated muriatic acid (spirit of salt of commerce).
Sulphuretted hydrogen gas will become disengaged from the materials in
abundance, and pass through the water in the vial (_c_). Let the
extrication of the gas be continued for about five minutes; and if the
minutest quantity of lead be present, the water will acquire a
dark-brown or blackish tinge. The extrication of the gas is facilitated
by the application of a gentle heat.

The action of the sulphuretted hydrogen test, when applied in this
manner, is astonishingly great; for one part of acetate of lead may be
detected by means of it, in 20000 parts of water.[24]

Another test for readily detecting lead in water, is sulphuretted
chyazate of potash, first pointed out as such by Mr. Porret. A few drops
of this re-agent, added to water containing lead, occasion a white
precipitate, consisting of small brilliant scales of a considerable
lustre.

Sulphate of potash, or sulphate of soda, is likewise a very delicate
test for detecting minute portions of lead. Dr. Thomson[25] discovered,
by means of it, one par