HOWARD'S METHOD OF VAPORISATION. 171 



IX. HOWARD'S METHOD OF VAPORISATION. 



THE principle of Mr. Howard's apparatus, which is of recent date, may be gathered from the 

 following description, which is abstracted from the specification of his patent. 



In the ordinary method of generating steam by means of boilers, a body of water is exposed 

 to a large surface of metal, presenting to it a comparatively low degree of heat ; and the tem- 

 perature of the water bearing a constant relation to the density or pressure of the steam, the 

 rapidity of evaporation is limited thereby. In my process of VAPORISATION the power of the 

 engine is derived from the vaporisation of the least possible quantity of water on a small 

 surface, heated to and maintained at such temperature (about 400 Fahrenheit) as will vaporise 

 the water with the utmost rapidity ; the steam so formed having a high temperature, but 

 relatively a low density or pressure. And by the interposition of mercury, or other medium 

 of the like effect, the surface exposed to the fire is preserved from the injury that would 

 otherwise arise from a strong local heat ; and the deposit of salts or other impurities on the 

 vaporising surface is prevented by the continued use of the same water. And in my engine 

 other liquids, as alcohol for instance, may be substituted for water. 



A circular, or otherwise formed wrought-iron plate, is fixed horizontally over a fire con- 

 structed to burn coke, anthracite coal, or other fuel of the like nature, and urged by a blowing 

 machine subject to regulation. The area of the grate is about a fifth of a square foot per 

 horse power of the engine. The area of the plate exposed to the action of the fire need not 

 exceed three-fourths of a square f :ot per horse power. A second plate is fixed above this, 

 and has securely fitted into it, and throughout its surface, a number of thin wrought-iron cups 

 or short cylinders, about two inches in diameter, closed at bottom, and reaching to within a 

 little distance of the interior of the lower plate, by which means the upper surface is increased 

 to about four times the lower. Both plates are slightly curved downwards. A true and 

 secure joint is formed at the circumference of the plates, by bolting them to a strong ring 

 about three inches deep, and which fixes them at a corresponding distance apart. The inter- 

 mediate space (being under and around the cups) is entirely filled with mercury or a soft 

 amalgam. A small box of iron communicates with it to allow of its expansion when heated, 

 and the steam being admitted to this portion of the mercury, the pressure is equalized above 

 and below the upper plate and cups. A thermometer indicates the temperature of the mer- 

 cury, which must never be permitted to rise much above five hundred degrees Fahrenheit, 

 nor should it be allowed, while the engine is at work, to fall below three hundred and fifty 

 degrees, the fire, or the quantity of water injected (as presently described) being regulated 

 accordingly. A nosle or rose, constructed to disperse the water as equally as possible, is 

 fixed above the upper plate, and, by means of a pump, throwing at intervals, a small quantity 



