296 POPULAR SCIENCE MONTHLY. 



or closed crucible or tube containing the substance heated. This is the 

 simplest form of laboratory furnace. Various modifications are' used, 

 but in all the size is small and the arrangement simple. A powerful arc 

 plays in the smallest possible cavity with the object of attaining the 

 maximum of temperature, expense and duration of material being sec- 

 ondary considerations. Lime and magnesia are the best materials, be- 

 cause they are at the same time the most refractory substances available 

 and are poor conductors of heat. A furnace top one and one half inches 

 thick may be heated by so powerful an arc that the melted quick lime 

 drips from the inner surface, while the outer surface is scarcely warm to 

 the touch of the hand. • Moissan has utilized in these little furnaces cur- 

 rents of electricity of varied strength, the lowest being that given by a 

 four horse power dynamo, the highest that generated by three hundred 

 horse power. The highest temperatures obtained were about 3,500° 

 centigrade (6,300° Fahrenheit), with the heat constantly increasing; 

 the limit to the obtainable temperature — as far as the experimental evi- 

 dence showed — was merely the lack of any known substance refractory 

 enough to bear the heat; for at the temperature mentioned quick lime 

 and magnesia not only melt but are changed into gases, so that the fur- 

 nace was filled with the vapors of its own material. 



The effect of the heat on single substances is very interesting. 

 Refractory metals, such as iron, manganese, uranium, platinum, melt 

 rapidly and then become gaseous; the most refractory non-metallic 

 elements, silicon, boron, carbon, are also changed into the gaseous 

 form. Very refractory compounds are broken down into simpler ones. 

 Magnesium pyrophosphate yields phosphorus, magnesium oxide and 

 oxygen. Asbestos — a magnesium silicate — gives as chief product mag- 

 nesium silicide; the other substances formed being silicon, silicon 

 dioxide and a little magnesium oxide. 



Such are the astounding changes wrought by simple heat upon 

 those substances which we are accustomed to regard as infusible. It 

 must be remembered that the range of temperature which chemists 

 employ in ordinary laboratory work is not very great and that the 

 conditions of work in the laboratory and of nature's work on the 

 earth's surface at the present day favor the formation of two 

 classes of compounds — the oxides and their hydrates. Although 

 air is a mixture consisting mainly of four parts of nitrogen and 

 one of oxygen, atmospheric nitrogen is generally inert at ordinary 

 temperatures, and it is the oxygen of the air which is the more impor- 

 tant factor in the growth of living things and in changes in lifeless 

 matter. Water, a compound of oxygen and hydrogen, is present every- 

 where, either in the liquid form or as vapor in the air; even in the flame 

 of the hottest fires there is water vapor in abundance, since water is 

 one of the chief products of combustion of most forms of fuel. Is it a 



