Dr. Stevenson recommends as a convenient test for the presence of zinc in potable waters, the addition of potassium ferro-cyanide to the filtered and acidulated water. Zinc gives a faint white cloud, or a heavier precipitate when more is present.

Tests For Copper

1. Yellow prussiate of potash is a test for ascertaining the presence of copper in water. Draw a small quantity of the suspected water; then drop into it a small piece of the potash; should copper be present, the water assumes a reddish-brown color. Should iron be present, the water will become black. Prussiate of potash is a deadly poison.

2. To detect a copper percentage, add a little filing dust of soft iron to the water, leave them in for a few minutes, and add a few drops of sal-ammonia. A blue coloration betrays the presence of copper. (Industrial Record.)

The use of water containing copper, even in so small a quantity as one-tenth of a grain per gallon (1 in 6,000,000), is very dangerous and should be rejected.

Test For Sulphur

The presence of sulphur may be discovered by introducing into a bottle containing the water to be tested a small quantity of quicksilver, corking it and allowing it to stand a few hours. If the mercury assumes a dull appearance, and is resolved into dusty fragments on being shaken, sulphur is combined with the water.

Test For Hydrogen Sulphide

Shake some of the water in a clean bottle, and observe the odor, which is the same as that emitted by the solution of sulphide of soda (a smell like rotten eggs).

Test For Iodine And Bromine

Precipitate the water with an acid solution of nitrate of silver, mix the precipitate with cyanide of silver, and pass a current of dry chlorine over it, when it forms iodide or bromine of cyanogen. (Henry and Humbert.)