Explosives are manufactured articles; explosiveness is a property of certain arrangements of certain quantities of certain elements: so far as experiments have gone, it has not been found possible to add the property of radio-activity to an inactive substance, or to remove the property of radio-activity from an active substance; the cessation of the radio-activity of an active substance is accompanied by the disappearance of the substance, and the production of inactive bodies altogether unlike the original active body.
Radio-active substances are constantly giving off energy in the form of heat, sending forth _rays_ which have definite and remarkable properties, and producing gaseous _emanations_ which are very unstable, and change, some very rapidly, some less rapidly, into other substances, and emit _rays_ which are generally the same as the rays emitted by the parent substance.

In briefly considering these three phenomena, I shall choose radium compounds as representative of the class of radio-active substances.
Radium compounds spontaneously give off energy in the form of heat.

A quantity of radium chloride which contains 1 gram of radium continuously gives out, per hour, a quantity of heat sufficient to raise the temperature of 1 gram of water through 100 deg.

C., or 100 grams of water through 1 deg.

C.The heat given out by 1 gram of radium during twenty-four hours would raise the temperature of 2400 grams of water through 1 deg.