of a balloon of six liters capacity, in the interior of which an electric flame is kept alight by means of a transformer, while a jet of caustic alkali forms a fountain in the interior, gives good results. By its help, seven or eight liters of mixed gases can be made to combine per hour.

Such experiments show the inactive nature of the argon group of gases towards an electro-negative element, oxygen. The gases are absolutely incombustible. No other elements can withstand such treatment, save platinum and its congeners, and gold. But even these metals combine with fluorine or chlorine, when heated in a current of one or other gas. Argon, however, is wholly unaffected when electric sparks are passed through its mixture with chlorine or fluorine, the two other most electro-negative elements. To them, too, it shows itself completely indifferent.

A more convenient method of separating the nitrogen from its admixture with argon in atmospheric air is by means of red-hot magnesium. The metal magnesium,Fig. 3.which is now made on a considerable scale for photographic and signaling purposes, is a white, silvery metal, which can be planed or turned into shavings. In the early experiments, a measured quantity of atmospheric nitrogen, dried by passing over suitable drying agents, was brought into contact with magnesium turnings, heated to redness in a tube of hard glass. It has been found, however, by M. Maquenne, that the metal calcium, which, for this purpose is most easily produced by heating together a mixture of magnesium filings and pure dry lime, is a more efficient absorbing agent for nitrogen, for it does not require such a high temperature, and can be effected without danger of melting the glass tube. Indeed, the operation is a very easy one, and can be carried out with the very simple apparatus shown in Figure 3. M. Guntz has also found that lithium, an element belonging to the same column in the periodic table as sodium and potassium, is an exceedingly good absorbent for nitrogen, for it tarnishes in nitrogen even at atmospheric temperature, owing to the formation of a nitride.

On a large scale, the magnesium turnings are contained in iron tubes, and the gas-holders are made of copper or of galvanized iron. By this means, fifteen liters of argon were separated from about two cubic yards of air.

The inactivity of argon in contact with such highly electro-positive elements as lithium, magnesium and calcium again demonstrates its