Observe attentively the steam that escapes from the spout of a tea-kettle, at the moment the water begins to boil, and you will perceive the steam to be condensed in minute drops on the interior edges of the spout. A few moments afterwards, provided the water continue to boil, the spout of the kettle will become perfectly dry; and, at the same time, close to it, there will be a certain space, say from one-half to three-fourths of an inch, throughout which not a particle of steam will be perceptible. This may be easily explained. When the water in the kettle begins to boil, the spout being cooler than the steam issuing from it, a portion of that steam is condensed. As more steam escapes, the metal soon becomes as hot as the steam, will no longer condense it, and the spout becomes dry. By this time the steam will displace the air immediately opposite the orifice of the spout, whence it will issue dry and invisible. As it is cooled by mixing with the surrounding air, it assumes its well-known cloudy appearance. [Illustration] [Illustration: FIRE, WATER, AND AIR.] [Illustration] FIRE, WATER, AND AIR. COLOURED FLAMES. A VARIETY of rays of light is exhibited by coloured flames, which are not to be seen in white light. Thus, pure hydrogen gas will burn with a blue flame, in which many of the rays of light are wanting. The flame of an oil-lamp contains most of the rays which are wanting in sunlight. Alcohol, mixed with water, when heated or burned, affords a flame with no other rays but yellow. The following salts, if finely powdered, and introduced into the exterior flame of a candle, or into the wick of a spirit-lamp will communicate to flame their peculiar colours: Muriate of Soda (common salt) Yellow. Muriate of Potash Pale violet. Muriate of Lime Brick red. Muriate of Strontia Bright crimson. Muriate of Lithia Red. Muriate of Baryta Pale _apple_-green. Muriate of Copper Bluish green. Borax Green. Or, either of the above salts may be mixed with spirit of wine, as directed for Red Fire. YELLOW FLAME. Burn spirits of wine on common table salt or saltpetre. ORANGE-COLOURED FLAME. Burn spirit of wine on chloride of calcium, a substance obtained by evaporating muriate of lime to dryness. EMERALD GREEN FLAME. Burn spirit of wine on a little powdered nitrate of copper. INSTANTANEOUS FLAME. Heat together potassium and sulphur, and they will instantly burn very vividly. Heat a little nitre in a fire-shovel, sprinkle on it flour of sulphur, and it will instantly burn. If iron filings be thrown upon red-hot nitre, they will detonate and burn. Pound, separately, equal parts of chlorate of potash and lump sugar; mix them, and put upon a plate a small quantity; dip a thread into sulphuric acid, touch the powder with it, and it will burst into a brilliant flame.