must be mixed by adding the acid slowly to the water; never the water to the acid. The combination of acid and water enters at once into reaction and always generates heat, and the result of adding water to acid would be small explosions. There would be danger of the acid flying on one's clothes or into the eyes. The mixture should never be stronger than six parts of water to one of acid.

The beginner will observe from the above that the generator cannot be crowded by making the acid solution strong. Hydrogen is a peculiar gas and also a dangerous one for one ignorant of its peculiarities to experiment with, and in order to thoroughly understand it the following experiments should be demonstrated, which can be done with little expense. The beginner should note the result of each experiment as demonstrated, and carefully commit the same to memory for future reference.

Experiment 1.

Test for Hydrogen.—Fill a small jar or wide mouthed bottle with hydrogen. This is done by 22first filling the bottle with water, inserting the end of the tube from the hydrogen generator, having first exhausted the air in the tube, then quickly inverting the bottle and placing the neck, Fig. 2, in a pan of water (A); the water will stay in the bottle. Now turn on the hydrogen. The gas, being lighter than water, will rise to the top of the bottle (B), drive out the water, and replace it with pure hydrogen, which should be free from air. Remove the bottle from the pan of water, keeping it inverted. Thrust a lighted splint into the bottle. The gas will light and burn at the mouth of the bottle. If the splint is thrust far into the bottle it will go out. Drops of water collect in the bottle. Burning is a union with oxygen; therefore, the burning of the hydrogen shows that it has an affinity for oxygen. The splint goes out because