_Carbon Monoxide, or Carbonic Oxide. Symbol CO._--This is formed when carbon is burnt with an insufficient supply of oxygen, or when carbonic acid gas is passed over some carbon heated to redness. This gas is continually being formed in our furnaces and fire-places; at the lower part of the furnace, where the air enters, the carbon is converted into carbonic acid, which in its turn has to pass through some red-hot coals, so that before reaching the surface it is again converted into carbonic oxide; over the surface of the fire this carbonic oxide meets with a fresh supply of oxygen, and is then again converted into carbonic acid. The peculiar blue lambent flame often observed on the surface of our open fire-places is due to the combustion of carbonic oxide, which has been formed in the way we have just described. Carbonic oxide is a colorless, tasteless gas, which differs from carbonic acid by being combustible, and by not having any action on lime water.--_Brewers' Guardian._ * * * * * SEYFFERTH'S PYROMETER. The thermometers and pyrometers usually employed are almost all based on the expansion of some fluid or other, or upon that of different metals. The first can only be constructed with glass tubes, thus rendering them fragile. The second are often wanting in exactness, because of the change that the molecules of a solid body undergo through heat, thus preventing them from returning to exactly their first position on cooling. [Illustration: Fig. 1.--Pyrometer with Electric Indicator.] The principle of the Seyfferth pyrometer is based on the fact that the pressure of saturated vapors, that is, vapors which remain in communication with the liquid which has produced them, preserves a constant ratio with the temperature of such liquid, while, on the other hand, the temperature of the latter when shut up in a vessel will correspond exactly with that of the medium into which it is introduced. [Illustration: Fig. 2.--Method of Mounting by means of a cone on vacuum apparatus.] [Illustration: Fig. 3.--Mounting by means of a sleeve on vacuum apparatus.]