These are substances employed to determine the name or character of any other substance, or to detect its presence in compounds. They are used in both the solid and fluid state; generally the latter, when they are known as liquid tests. Their application as reagents is called testing. . For this purpose they are commonly added drop by drop to the liquid to be tested, contained in a test-tube or test-glass. A simple way of employing them is to place a few drops or a small portion of the liquid or substance for examination on a slip of common white glass, and to add to them a drop of the test liquid. By placing the glass over a sheet of white paper, the effect will be rendered more perceptible.

A number of tests, not included here, referring to substances which hold a prominent place in some special process, have been introduced in immediate connection with the description of those substances, and will be found in the index under the head of the article to be tested.

4373. Test for Chicory in Coffee

4373. Test for Chicory in Coffee. Place a spoonful of ground coffee gently on the surface of a glass of cold water. The pure coffee will float for some time, and scarcely color the water; the chicory, if any be present, rapidly absorbs the water and sinks to the bottom, communicating a deep reddish-brown tint as it falls.

Or a spoonful of ground coffee may be placed in a small bottle of cold water, and shaken for a moment; if the sample of coffee is pure, it will rise to the surface and hardly tinge the water, whilst if the coffee is adulterated with chicory, the latter will fall to the bottom and color the water as before. A similar coloration of the water will be produced, however, if the coffee be adulterated with burnt sugar, which is the basis of the so-called " coffee essences or extracts."

4374. To Test Tea

4374. To Test Tea. Pure China tea is not turned black by being put into water impregnated with sulphuretted hydrogen gas, nor does it tinge spirit of hartshorn blue. The infusion is amber-colored, and is not reddened by adding a few drops of oil of vitriol to it.

4375. To Detect Copper in Liquids

4375.    To Detect Copper in Liquids. Spirit of hartshorn turns them blue. Therefore tea has not been dried on copper if an infusion of it is not turned blue by this mixture. Cider, being passed through brass pots, is detected by this experiment.

4376. To Detect Watered Milk

4376.    To Detect Watered Milk. The cheapest and easiest method of adulterating milk is by adding water, and we may readily ascertain the exact extent of adulteration by the following plan. If a glass tube, divided into 100 parts, be filled with milk and left standing lor 24 hours, the cream will rise to the upper part of the tube, and occupy from 11 to 13 divisions, if the milk is genuine.

4377. To Detect Chalk in Milk

4377.    To Detect Chalk in Milk. Dilute the milk with water; the chalk, if there be any, will settle to the bottom in an hour or two; put to the sediment an acid, vinegar for instance, and if effervescence take place it is chalk.