MECHANICS AXD USEFUL ARTS. 55 



pressure, coals were applied liberally, and in seven minutes the steam gauge 

 indicated thirty-five pounds, the smoke during this period being simply of a 

 vaporous transparent character. There were two sixty-horse boilers in use, 

 each having two flues and furnaces. The usual plan was to coal the fur- 

 naces under each boiler alternately, but in this instance it was done simul- 

 taneously, yet the smoke was so trivial that the observers expressed them- 

 selves fully satisfied with the result. In the second trial the steam was 



i 



raised to a high pressure more rapidly, the smoke still being suppressed. 

 Sawdust and other materials were also thrown upon the furnace, and dense 

 smoke produced, but it was so effectually consumed behind the perforated 

 bridge that the top of the chimney scarcely indicated the existence of a fire. 



REQUISITES FOR A PERFECT HOT AIR FURNACE. 



The Committee of the Boston Mechanics Association appointed to report 

 on the hot air furnaces exhibited at the last Fair, call attention in their Re- 

 port to the fact, that all the arrangements for the warming of dwellings, 

 lately brought forward, present no important deviation from the stereotyped 

 ideas which have continued for many years to guide inventors in this branch 

 of construction. Such a result, hoAvever, say the Committee, can hardly 

 be regarded as surprising, or as discreditable to the inventive genius of those 

 Avho have occupied themselves Avith the subject, Avhen it is remembered that 

 there are few problems in practical science involving such A r arious and com- 

 plex conditions as that of producing a Avarming apparatus Avhich shall be 

 at once efficient, economical, and healthful in its operation. The inherent 

 difficulties of this problem Avill be best illustrated by a brief summary of the 

 functions and requisites of a perfect hot air furnace. 



1st. To secure the efficiency and economy of such a furnace, two things 

 are necessary. 



First, The fuel employed should be as completely as possible consumed in 

 the body of the apparatus, leaving little or none to escape, in the form of 

 combustible gas, or smoke, or to remain behind in the A'itrified condition of 

 clinker. A combustion thus complete can only be attained through a nice 

 adjustment and distribution of the draft, and such form and adaptation of 

 the stove chamber and contiguous cavities as Avill detain the evolved com- 

 bustible gas until it shall be entirely burned. 



The fire pot should not be a focus of intense heat, but the heat generated 

 in it should be rapidly conducted and radiated from it. In the general 

 adaptation, a regular combustion of an adequate quantity of fuel should be 

 provided for, and the regulation of the consumption ought to depend on the 

 proportion of air admitted to sustain it. It is a very common impression 

 that smoke-consuming furnaces and close air stoves are economical in the 

 consumption of fuel, as the escaping products haA-e a low temperature. A 

 careful examination of the amount of surface Avill teach any one that this, 



/ 



with the advantage arising from retarded draft, sufficiently accounts for the 

 fact that under the production of really less heat, more warmth is radiated. 

 The close stoves in fact distil the fuel, or allow of only an imperfect com- 



