Very frequently it is important to the dentist to know whether his peroxide of hydrogen, which is so liable to change, is still good or has become decomposed; or whether his solution of bichloride of mercury has become inert by the reducing action of organic matter in the water under the influence of sunlight. And so of many other chemicals used in the dental office which are apt to change in strength.

Prof. Chas. Mayr, of Springfield, Mass., has prepared a series of test-papers, which will enable the dentist to learn quickly and accurately whether his preparations are good or worthless, and without the use of cumbersome methods. They are put up in neat little books, each containing eight different papers (of some, like litmus, several papers are provided), affording sixty-four different reactions. The papers are as follows:

Phenyl-Carbinol, for strong acids and alkalies.

Turmeric, for alkalies.

Sulphide, for solution of metals.

Potassium Iodide, for H2O2, bichloride 1/500.

Iodide Starch, for hydrogen peroxide.

Litmus, for weak acids and alkalies.

Erythorine, for salts and alkalies.

Lacmoid, substitute for litmus, not affected by carbonic acid.

Each paper has printed upon it the reactions it gives, so that even the inexperienced have a safe guide as to its uses.