When the demand for it arises, hydrogen gas can be made as cheaply as water gas itself, and when time is ripe for a fuel gas for use in the house, it is hydrogen and not water gas which will form its basis. With carbureted water gas and 20 per cent. of carbon monoxide we are still below the limit of danger, but a pure water gas with over 40 per cent. of the same insidious element of danger will never be tolerated in our households. Already a patent has been taken by Messrs. Crookes and Ricarde-Seaver for purifying water gas from carbon monoxide, and converting it mainly into hydrogen by passing it at a high temperature through a mixture of lime and soda lime, a process which is chemically perfect, as the most expensive portion of the material used could be recovered; but in the present state of the labor market it is not practical, as for the making of every 100,000 cubic feet of gas, fifteen tons of material would have to be handled, the cost of labor alone being sufficient to prevent its being adopted; moreover, hydrogen can be made far cheaper directly. From the earliest days of gas making, the manufacture of hydrogen by the passage of steam over red-hot iron has been over and over again mooted, and attempted on a large scale, but several factors have combined to render it futile. In the first place, for every 478.5 cubic feet of hydrogen made under perfect theoretical conditions never likely to be obtained in practice, 56 lb. of iron were converted into the magnetic oxide, and as there was no ready sale for this article, this alone would prevent its being used as a cheap source of hydrogen; the next point was that when steam was passed over the red-hot iron, the temperature was so rapidly lowered that the generation of gas could only go on for a very short period, while, finally, the swelling of the mass in the retort and fusion of some of the magnetic oxide into the side renders the removal of the spent material almost an impossibility. These difficulties can, however, be got over. Take a fire clay retort, six feet long and a foot in diameter, and cap it with a casting bearing two outlet tubes closed by screw valves, while a similar tube leads from the bottom of the retort. Inclose this retort by a furnace chamber of iron lined with fire brick, leaving a space of two feet six inches round the retort, and connect the top of the furnace chamber with one opening at the top of the upright retort, while air blasts lead into the bottom of the furnace chamber, below rocking fire bars, which start at bottom of the retort, and slope upward, to leave room for ash holes closed by gas tight covers. The retort is filled with iron or steel borings, alone if pure hydrogen is required, or cast into balls with pitch if a little carbon monoxide is not a drawback, as in foundry work. The furnace chamber is now filled with coke, fed in through manholes, or hoppers, in the top, and the fuel being