Progress of Invention. 311 



more to our powers of manufacturing iron and steel, on the large 

 scale, than the invention of the steam-hammer. Without it, in 

 reality, our other improvements in metallurgy would have been 

 deprived of nearly all their value ; since the great necessity at the 

 present day in engineering is the forging of enormous masses in a 

 sound and reliable manner, which would be impossible even with 

 the best forms of the old tilt hammer. The steam-hammer has been 

 brought to an extraordinary degree of perfection, but is likely in 

 many instances to be superseded by the still more simple application 

 of the elasticity of the air as a substitute for steam. The atmo- 

 spheric, like the usual form of steam-hammer, has the mass with 

 which the blow is struck attached to the lower end of a rod, which 

 is fixed to a piston that moves up and down within a cylinder. 

 But instead of this piston being raised and depressed by the intro- 

 duction of steam below and above it, the cylinder itself is alter- 

 nately made to ascend and descend, by being connected with a 

 revolving crank. When the cylinder is raised, the air which has 

 been admitted beneath the piston is compressed until its elasticity 

 is sufficient to lift the piston and the hammer attached to it. 

 When the cylinder is depressed, the air above the piston is com- 

 pressed, and, by its elastic power drives down the piston and 

 hammer with great force and velocity. The piston is prevented 

 from falling, before the elasticity of the air above has begun to act 

 upon it, by the rapidity with which the compressions above and 

 below succeed each other. 



Production op Nitride of Iron. — Nitride of iron, which has 

 been ascertained to be the only compound of nitrogen and iron, 

 and is an ammonium in which the whole of the hydrogen is replaced 

 by iron, may be conveniently obtained by passing ammonia over 

 pure protochloride of iron, at a temperature which is just sufficient 

 to drive off in vapour the chloride of ammonium that is produced. 

 The residue is nitride of iron in thin laminas, or a grey powder. It 

 is decomposed by a high temperature, as also by chlorine, acids, etc. 

 If pulverized, which is easily done, and thrown into the flame of a 

 spirit lamp, it burns with the production of brilliant scintillations. 

 Heated in hydrogen, the nitrogen is driven off, and the softest and 

 purest iron known is left behind. 



A New and Powerful Light, — A brilliant light, which answers 

 well for photography, is obtained by M. Carlevaris, by throwing on 

 chloride of magnesium the flame obtained by means of a jet of coal 

 gas, and a mixture of atmospheric air with one-tenth of its volume 

 of oxygen. Pifty litres of coal gas, and about one hundred of 

 atmospheric air, used in this way, per hour, were found to illuminate 

 an immense apartment so thoroughly that it was possible to read 

 with ease in every corner of it. 



Miscellaneous. — The Sewage Plant. — The nature and habits of 

 this curious plant, which is such an obstacle to the filtration of 

 sewage, have lately been investigated with considerable attention. 

 It makes its appearance in the globular or filamentous form, accord- 

 ing to circumstances, and is a species of fungus, of a drab colour, 

 passing into black. Cool weather is more favourable to its produc- 



