PRACTICAL UTILITY OF PNEUMATICS. 



phere, with a force equal to 15 pounds on every 

 square inch, presses the pieces firmly together. 

 A knowledge of this principle will suggest the 

 propriety of filling up every opening or crevice, 

 and continuing the pressure for some time, as 

 the air, wherever it gains admission, has a ten 

 dency, by its elastic force, to loosen every spe 

 cies of cement. The same principle might di 

 rect bricklayers arid masons, in building either 

 stone or brick- walls, in suggesting the propriety 

 of filling up every crevice with the most tena 

 cious cements, so as to prevent the access of 

 the external air to the interior of the walls. 

 For there can be no question that the firmness 

 and stability of our houses and garden-walls de 

 pend, in part, upon the pressure of the atmos 

 phere, after the interior crevices are thoroughly 

 filled up. An extensive knowledge of this 

 science would likewise direct them to the proper 

 mode of constructing the flues of chimneys, so 

 as to prevent that most disagreeable of all cir 

 cumstances indwelling houses, smoky chimneys. 

 From ignorance of the effects of heat, of the 

 experiments that have been made on rarefied 

 air, and their relation to our common fires, of 

 the proper dimensions of funnels, of the effects 

 of winds and currents of air, of the proper 

 height and width of chimneys, of the method 

 of promoting a good draught, and making the 

 air pass as near the fire as possible, and various 

 other particulars requisite to be attended to in 

 the construction of fire-places and their flues ; 

 many dwelling-houses have been bungled, and 

 rendered almost uninhabitable. The workmen, 

 m such operations, without any rational princi 

 ple to guide them, carry up funnels in the easiest 

 way they can, according to the practice of&quot; use 

 and wont,&quot; and leave the tenants or proprie 

 tors of the houses they erect to get rid of their 

 smoke in the best way their fancy can con 

 trive. Whereas, were chimneys and their flues 

 constructed according to the principles of 

 science, they might be rendered, almost with 

 certainty, completely efficient for the pur 

 pose intended. 



To all who are acquainted with the nature 

 and properties of elastic fluids, it must be ob 

 vious, that the whole mystery of curing smoky 

 chimneys consists in finding out and removing 

 the accidental causes which prevent the heated 

 smoke from being forced up the chimney by the 

 pressure of the cool or heavier air of the room. 

 These causes are various ; but that which will 

 be found most commonly to operate is, the bad 

 construction of the chimney in the neighbourhood 

 of the Jim-place. &quot; The great fault,&quot; says Count 

 Rumford, &quot; of all the open fire-places now in 

 common use is, that they are much too large, 

 or rather it is the throat of the chimney, or the 

 lower part of its open canal, in the neighbour 

 hood of the mantle, and immediately over the 

 fire, which is too large.&quot; The following is a 



condensed view of some of the rules given on 

 this subject, by this ingenious practical philo 

 sopher, and which are founded on the principles 

 of science, and on numerous experiments: 1. 

 The throat of the chimney should be perpendi 

 cularly over thejire; as the smoke and hot va 

 pour which rise from a fire naturally tend up 

 wards. By the throat of a chimney is meant the 

 lower extremity of its canal, where it unites 

 with the upper part of its open fire-place. 2. 

 The nearer the throat of a chimney is to the 

 fire the stronger will be its draught, and the less 

 danger of its smoking ; since smoke rises in con 

 sequence of its rarefaction by heat, and the heat 

 is geater nearer the fire than at a greater dis 

 tance from it. But the draught of a chimney 

 may be too strong, so as to consume the fuel 

 too rapidly ; and, therefore, a due medium must 

 be fixed upon, according to circumstances. 3. 

 That/owr inches is the proper width to be given 

 to the throat of a chimney, reckoning across 

 from the top of the breast of the chimney, or the 

 inside of the mantle to the back of the chimney , 

 and even in large halls, where great fires are 

 kept up, this width should never be increased 

 beyond 4j or 5 inches. 4. The width given to 

 the back of the chimney should be about one- 

 third of the width of the opening of the fire-place 

 in front. In a room of a middling size, thirteen 

 inches is a good size for the width of the back, 

 and 3 times 13 or 39 inches for the width of the 

 opening of the fire-place in front. 5. The angle 

 made by the back of the fire-place and the sides 

 of it, or covings, should be 135 degrees, which 

 is the best position they can have for throwing 

 heat into the room. 6. The back of the chim 

 ney should always be built perfectly upright. 7. 

 Where the throat of the chimney has an end, 

 that is to say, where it enters into the lower 

 part of the open canal of the chimney, there the 

 three walls which form the two covings and the 

 back of the fire-place should all end abruptly, 

 without any slope, which will render it more 

 difficult for any wind from above to force its 

 way through the narrow passage of the throat 

 of the chimney. The back and covings should 

 rise 5 or 6 inches higher than the breast of the 

 chimney. 8. The current of air which, passing 

 under the mantle, gets into the chimney, should 

 be made gradually to bend its course upwards, 

 by which means it will unite quietly with the 

 ascending current of smoke. This is effected 

 with the greatest, ease and certainty, merely by 

 rounding qjf\\\e breast of the chimney, or back 

 part of the mantle, h.stead of leaving it flat or 

 full of holes and corners. Fig. 1 shjws the 

 section of a chimney on the common construc 

 tion, in which d e is the throat. Fig. 2 shows 

 a section of the same chimney altered and im 

 proved, in which d i is the reduced throat, four 

 inches in the direction of d t, and thirteen ; nchea 

 in a line parallel to the mantle. 



