MECHANICS AND USEFUL ARTS. 73 



the cold, fresh air then rising under it takes from it the excess of its heat, and 

 so becomes itself tempered, before it spreads in the room. The importance of 

 general ventilation again is strikingly illustrated by an occurrence which hap- 

 pened not long since in Glasgow. A large old building which had been form- 

 erly a cotton-mill, was fitted as a dwelling-house for persons of the working- 

 classes, and had nearly 500 inmates. Like all foul and crowded human 

 dwellings, fevers and kindred diseases soon became prevalent there. After a 

 time a medical man, who was interested, obtained permission from the pro- 

 prietors of a neighboring chemical works, in which there was a lofty and very 

 powerful chimney, to make an opening of one foot in diameter into the side of 

 the chimney for the ventilation of the lodging-house. He then connected with 

 this a main tube from the lodging-house, which had branches running along 

 all the passages or galleries, and from the ceiling of every separate room a 

 small tube communicated with these branches. Soon after, to the surprise as 

 well as to the delight of all concerned, severe diseases entirely disappeared 

 from the house, and never returned. 



s 



Now the chimney of the new fire-place, although not very tall has a venti- 

 lating power scarcely inferior to that of the Glasgow Chemical "Works. The 

 arrangement of the hood with its valve, as above described, by allowing only 

 unmixed and very hot smoke to enter the chimney, instead of, as in common 

 chimneys, smoke diluted with many times its volume of colder air, increases 

 the draught just as it does the heat of the chimney, and through an opening 

 then made into the chimney from near the top of a room, all the hot, foul air 

 in the room, consisting, perhaps, of the breath of inmates, smell of meals, 

 burned air from candles, lamps, etc., and which else accumulated and stagnated 

 at first near the top of the room, is immediately forced into the chimney and 

 away. This is strikingly proved by placing, near the ventilating opening, a 

 light body, as feathers or shreds of paper, suspended to a thread, and seeing 

 with what force it is drawn into the opening. 







ON THE CONSUMPTION OF SMOKE. 



The subject of the consumption of smoke continues to be frequently dis- 

 cussed in most of the scientific journals and circles of England. Mr. Muir, 

 in a communication to the Society of Arts, states that the statements often 

 made, that from seventy-five all the way down to ten per cent, of fuel can be 

 saved by the consumption of smoke, are not founded upon any reliable facts. 

 "We have never seen any evidence to satisfy that the direct saving from the 

 burning or prevention of smoke was over five per cent., and in some cases no 

 difference has resulted in the quantity of fuel consumed, whether the smoke 

 was consumed or not. The conditions requisite for combustion are, that the 

 subjects of combustion the fuel and the oxygen should be brought in con- 

 tact and subjected to heat sufficient to unite them. But the smoke discharged 

 from furnaces is generally the result of imperfect combustion consequent upon 

 the stoppage of the process after it has been begun. The stoppage, in many 

 cases, is caused by deficient draught ; from want of air the heat necessary for 

 combustion is not maintained. But a common cause of dense volumes of 



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