Fig. 22.
The Magic Writing.—Fill a deep tumbler with water, and add a few crystals of iodide of potassium and a few drops of sulphuric acid. The liquid will remain perfectly clear like water. On some strips of white cardboard write various names with starch paste; when dry these will be invisible. On dipping the cardboard into the liquid the name will appear in blue writing, owing to the formation of starch iodide, which is blue. By previously preparing the names of those present at the experiment, by a little manipulation you can, to the astonishment of the audience, produce any name called for.
Producing Smoke at Will.—Two glass cylinders are the best for this, but ordinary tumblers will do. With a separate feather make the inside of each tumbler quite wet, one with hydrochloric acid, and the other with liquid ammonia. Both glasses appear to be quite empty, and nothing occurs. But on bringing the mouths of the two vessels together, a thick white smoke is at once developed. The hydrochloric acid gas and the ammonia gas unite chemically, and form the solid white powder known as sal-ammoniac. (See Fig. 23.)
Fig. 23.
A Novel Fountain.—This is a pretty experiment, and owes its action to the fact that ammonia gas is very soluble in water. In a basin place some water. Fit up a flask with a small-bore glass tube, about eighteen inches long, as shown. The end entering the flask should be drawn out so that there is only a small opening. In the flask place about a teaspoonful of liquid ammonia, and heat it over a spirit lamp. As soon as the liquid boils a large amount of ammonia gas is disengaged, and fills the flask and the tube. Now close the tube by means of the finger, and invert the flask over the basin of water. When the end of the tube is under the water remove your finger, and then, as the water dissolves the gas, it will rise in the tube, and will presently play into the flask like a fountain until the flask is full. (See Fig. 24.)
Fig. 24.