MECHANICS AND USEFUL ARTS. 75 



In another communication to the London Society of Arts, Mr. "Woodcock 

 maintained that the simplest means of preventing the formation of smoke was 

 by providing for an ample supply of oxygen in a condensed state, in the form 

 of cold air, to the fuel in the fire bars ; and by administering such further 

 supply of oxygen to the heated gases as might be necessary for their complete 

 combustion while hi contact with the boiler ; this latter supply being given at 

 such a temperature as would insure the successive ignition of the gases as 

 they were evolved. Thus, by establishing nearly perfect primary combustion, 

 the quantity of smoke evolved is reduced to a minimum, of which no visible 

 trace ever reached the summit of the chimney. 



An apparatus, by which this desirable end was attained, was described to 

 consist of two parts, each being the addition of a very simple apparatus to the 

 ordinary boiler furnace. The first of these was a double set of thin iron bars, 

 lying horizontally in the direction of their length parallel to each other, im- 

 mediately beneath the grate in the ash-pit. Each set of bars resembled a 

 Venetian blind in its arrangement, the bars being inclined at an angle of 45 

 to the horizon in the direction of their width. The bars of the two sets were 

 thus inclined in opposite directions, and being so close together that a vertical 

 straight Line could not pass between any adjacent pair of them, yet far enough 

 apart to allow ah 1 cinders to fall freely through, andj:he air to pass freely up- 

 ward to the fire. The bars were of the same length as the grate, so as to 

 extend from front to back. The effect of this arrangement is to screen the 

 ash-pit completely from the heat radiated directly downward from the grate, 

 and so that scarcely any would pass through by reflection. In fact, not a ray 

 of heat could reach the ash-pit from the furnace without suffering four reflec- 

 tions from rough iron surfaces, which would leave a mere shadow of a ray for 

 further progress. Thus a large quantity of heat, which would otherwise be 

 radiated out of the furnace into the ash-pit, thence reflected, and so lost, was 

 saved for the boiler. The ash-pit also was only slightly heated by the cinders 

 which fell through ; and this source of heat might be reduced to any extent 

 by frequently removing the rubbish from the pit. Another consequence was, 

 that the air passing from below through the grate, not being heated in the 

 ash-pit, entered the fire cold, and therefore not as it did from ordinary ash-pits 

 in a rarefied condition. By its coolness this air prevented, to some extent, 

 the burning of the grate bars ; and, by its unrarefied state, produced a more 

 intense and rapid combustion of the fuel after it had passed the bars. 



Another part of the contrivance was more especially the smoke-burning 

 apparatus. It consisted of a set of tubes, open at both ends, passing through 

 the furnace horizontally from front to back, and terminating within the wall 

 of the front of the bridge, with valves to regulate the access of air into the 

 tubes. The fire-bridge differed materially from that of an ordinary furnace. 

 It was hollow, and divided into two parts, the larger of which stood up from 

 below ; the other, which was more shallow, was hi contact with the boiler. 

 Between them all the products of combustion passed from the furnace. The 

 two parts communicated with each other by channels at the sides, and thus 

 formed together an annular chamber. The tubes before mentioned entered 

 the front wall of this chamber, and thus established a communication between 

 the interior and the outer air. The back wall, or plate, both of the upper and 



