The Romance of Modern Chemistry

GREAT DISCOVERIES St. Gotthard tunnel. For ordinary practical purposes, however, the explosive power of blasting gelatine is modified by introducing a certain amount of non-explosive absorbent material. Some discoveries have actually been made through an accident happening to the apparatus with which experi- ments were being carried out. This was the case with one important series of investigations into the behaviour of gases; and the famous chemist Graham has explained what it was that led him to make his wonderful experi- ments on gaseous diffusion. It appears that an earlier worker, Döbereiner, had occasion to prepare large quan- tities of hydrogen, and one day accidentally used as gas- holder a glass jar which had a tiny crack in it. Now it is a well-known fact that if an undamaged glass jar or tumbler containing hydrogen or air is in- verted in a dish of water, so that the level of the water outside and inside the jar or tumbler is the same, then no appreciable change will take place in the position of the water-level, even after a considerable time. But Dobereiner, to his great surprise, found that with his cracked jar inverted in water and containing hydrogen, the water gradually rose inside, inches in 12 hours, inches in 24 hours. It was left to Graham to give the correct interpreta- tion of this very striking observation. He showed that hydrogen, as the lightest known gas, can get through minute apertures more rapidly than any other gas, so that what occurred in Dobereiner’s cracked glass jar was an escape of hydrogen from the inside to the outside, accompanied by a slower entrance of air through the crack. As the hydrogen escaped more rapidly than the air got in, the pressure of the gas inside the jar was 338