cut in the annular flanges on the boss, and by a taper bolt or rivet through the tire and rim.  These spokes can be easily taken out and renewed when necessary by any unskilled person in a few minutes.  The spokes being twisted midway of their length give greater strength to the wheel and power to resist side strains in pulling out of deep ruts or holes, without increasing the weight.  The bosses and straps are made of malleable iron, in which the metal bushes are secured by means of a key with a washer screwed up on the front end.  They are also fitted with steel oil caps to the end of the bushes, which are provided with a small set screw, so that the cap need not be taken off when it is necessary to lubricate the wheel, as by simply taking out the set screw oil may be poured through the hole into the cap.  The set screw also forms a fulcrum for a key, so that the cap can be taken off or put on when required, as well as a means of preventing the cap being lost by shaking loose on rough roads.  In all hot and dry climates, the continued shrinking of wood wheels and loosening of the tires is a constant source of expense and inconvenience.  This wheel having a tire and rim entirely of metal does away with the difficulty, as the expansion and contraction are equal, consequently the tires need only be removed when worn out, and others can be supplied, drilled complete, ready for putting on, which can be done by any unskilled person.  The wheels of class B design are the same in principle of construction as those of class A, but they have cast metal bosses or naves, without loose bushes, and are suitable for general work and ordinary roads where the strains are not so severe.  The bosses or naves are readily removed in case of breakage, and they can be fitted with steel oil caps for lubricating.—­Iron.

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APPARATUS FOR THE PRODUCTION OF WATER GAS.

The apparatus shown in the accompanying engraving is designed for the manufacture of water gas for heating purposes, and is described in a communication, by Mr. W.A.  Goodyear, to the American Institute of Mining Engineers.

The generator, A, is lined with refractory bricks and is filled with fuel, which may be coal, coke, or any suitable carbonaceous material.  B and B’ are two series of regenerating chambers lined with refractory brick, and, besides, filled with refractory bricks piled up as shown in the figure.  The partitions, C and C’, are likewise of refractory brick, and are rendered as air-proof as possible.  Apertures, D and D’, are formed alternately at the base of one partition and the top of the adjacent one, in order to oblige the gases that traverse the series of chambers to descend in one of them and to rise in the following, whatever be the number of chambers in use.