THE HOTCHKISS REVOLVING GUN.
The Hotchkiss revolving gun, already adopted in the French navy and by other leading European nations, has been ordered for use in the German navy by the following decree of the German Emperor, dated January 11 last: "On the report made to me, I approve the adoption of the Hotchkiss revolving cannon as a part of the artillery of my navy; and each of my ships, according to their classification, shall in general be armed with this weapon in such a manner that every point surrounding the vessel may be protected by the fire of at least two guns at a minimum range of 200 meters."
THALLIUM PAPERS AS OZONOMETERS.
Schoene has given the results of an extended series of experiments on the use of thallium paper for estimating approximately the oxidizing material in the atmosphere, whether it be hydrogen peroxide alone, or mixed with ozone, or perhaps also with other constituents hitherto unknown. The objection to Schönbein's ozonometer (potassium iodide on starch paper) and to Houzeau's ozonometer (potassium iodide on red litmus paper) lies in the fact that their materials are hygroscopic, and their indications vary widely with the moisture of the air. Since dry ozone does not act on these papers, they must be moistened; and then the amount of moisture varies the result quite as much as the amount of ozone. Indeed, attention has been called to the larger amount of ozone near salt works and waterfalls, and the erroneous opinion advanced that ozone is formed when water is finely divided. And Böttger has stated that ozone is formed when ether is atomized; the fact being that the reaction he observed was due to the H2O2 always present in ether. Direct experiments with the Schönbein ozonometer and the psychrometer gave parallel curves; whence the author regards the former as only a crude hygrometer. These objections do not lie against the thallium paper, the oxidation to brown oxide by either ozone or hydrogen peroxide not requiring the presence of moisture, and the color, therefore, being independent of the hygrometric state of the air. Moreover, when well cared for, the papers undergo no farther change of color and may be preserved indefinitely. The author prepares the thallium paper a few days before use, by dipping strips of Swedish filtering paper in a solution of thallous hydrate, and drying. The solution is prepared by pouring a solution of thallous sulphate into a boiling solution of barium hydrate, equivalent quantities being taken, the resulting solution of thallous hydrate being concentrated in vacuo until 100 c.c. contains 10 grammes Tl(OH). For use the strips are hung in the free air in a close vessel, preferably over caustic lime, for twelve hours. Other papers are used, made with a two per cent. solution. These are exposed for thirty-six hours. The coloration is determined by comparison with a scale having eleven degrees of intensity upon it. Compared with Schönbein's ozonometer, the results are in general directly opposite. The thallium papers show that the greatest effect is in the daytime, the iodide papers that it is at night. Yearly curves show that the former generally indicate a rise when the latter give a fall. The iodide curve follows closely that of relative humidity, clouds, and rain; the thallium curve stands in no relation to it. A table of results for the year 1879 is given in monthly means, of the two thallium papers, the ozonometer, the relative humidity, cloudiness, rain, and velocity of wind.--G. F. B., in Ber. Berl. Chem. Ces.
THE AUDIPHONE IN ENGLAND.
The audiphone has been recently tried in the Board School for Deaf and Dumb at Turin street, Bethnal Green, with very satisfactory results--so satisfactory that the report will recommend its adoption in the four schools which the London Board have erected for the education of the deaf and dumb. Some 20 per cent. of the pupils in deaf and dumb schools have sufficient power of hearing when assisted by the audiphone to enable them to take their places in the classes of the ordinary schools.