A GERMAN AUTOMATIC FIRE ALARM.
The United States consul at Munich was recently present at an exhibition of the working of an automatic fire alarm in that city. He reports that the alarm operated within eight seconds after a small, pile of shavings had been set fire to in the corner of a room of ordinary size, the apparatus being placed close to the ceiling at the opposite end of the room in which the shavings were ignited. His description of the alarm, which costs retail about $2.86, and protects an area of some thirty or forty feet square, is as follows: “A glass tube, bent like the letter U, and having its ends closed is half filled with mercury, the upper half containing a highly volatile liquid—for instance, sulphuric ether. One of the upper parts of the glass tube is surrounded by a cover of some material which will not conduct heat. Hence a sudden rise of temperature affects only the other or free part of the glass tube, in case the temperature rises evenly, the whole apparatus is affected and no warning signal is given. If, however, the temperature in the room is suddenly raised, as by the outbreak ol a fire, the ether above the mercury in the glass tube, which is unprotected, evaporates, and the pressure of the generated vapors causes the mercury to sink in the tube while it rises in the opposite part. Both parts of the tube are fitted with an electric wire melted into the glass, so that, when the mercury stands equally high in both tubes, the electric current passes through, and the apparatus remains silent; hut, should a movement of the mercury take place because of a sudden rise of temperature, the electric circuit or contact is impeded, and any kind of an electric alarm may be set in motion at any distance, and at as many places as required. The apparatus also indicates impediments and interruptions of the electric current. The substances need no renewal, and the apparatus acts for an indefinite length of time.”