VOL. 5, No. 10
ODDEXPBRIMEMS
1333
ODD EXPERIMENTS The Synthetic Hatchery On page 1350 of the abstract section of this number a density demonstration is described. Many ingenious experiments based on density have been devised, but one of the simplest and most striking is that known as "the synthetic hatchery." For this experiment a glass cylinder or battery jar, a handful of mothballs, a handful of mossy zinc, some ordinary table salt, a little sulfuric acid, and f water are necessary. A solution of table salt and water is made up to such density that a mothball placed in the solution will just sink. The mossy zinc is placed in the bottom of the glass cylinder and sufficient salt solntion is added to fill the cylinder about three-fourths full. A little sulfuric acid is added to the solutionenough so that bubbles of hydrogen begin to appear on the surface of the zinc. The mothballs are then thrown in. At first the mothballs sink and as hydrogen is evolved tiny bubbles of the gas cling to them. Soon a mothball will have accumulated a sufficient coating of hydrogen to overcome the narrow margin of difference in density between itself and the surrounding salt solution, whereupon i t begins to rise to the surface. Bubbles of hydrogen may detach themselves as it rises and i t may return to the bottom without reaching the surface. If the mothball does reach the surface most of the hydrogen is lost there and it sinks to the bottom to repeat the process. When all the mothballs are in motion the effect is I similar to that sometimes observed in the hatchery tanks of an aquarium. Too many mothballs should not be used or they will collide with each other and lose their hydrogen coatings before rising very high in the solution. Too much add should not be added a t first. If there is not sufficient evolution of hydrogen or if the action begins to slow down after a time, a little more acid may be added.
A Chemical Weather Forecaster The change in color of a cobalt salt with changing degree of hydration discussed by Mr. Sorum on page 1287, may be made the basis for a chemical weather forecaster. Filter paper soaked in a solution of cobalt chloride and
dried constitutes the indicator. When atmospheric humidity is high the paper is pink; when humidity is low i t turns blue. The paper may be cut in the shape of a rain cape or umbrella and combined with a figure from an advertisement to form an attractive card.
