Economy of Fuel. 331 



taken off when the temperature of the entering gas was increasing, 

 when it was diminishing, and when stationary. It was likewise im- 

 portant to determine whether the proportion withdrawn when the 

 excess of the temperature in the entering gas above that of the room 

 was great, were the same as when it was less ; or whether, on the 

 contrary, the difference in the velocity of movement, of the gas due 

 to the difference of density, would sensibly increase the proportion 

 of that excess which would be withdrawn at the lower temperatures. 



Sq. inches. 

 The area of the convex vertical sides of the drum was 3091.4 



Do. of the two ends of do. - - - 923.6 



Do. of the pipe e from the drum to the thermometer t", 1234.6 



Total area, 5249.6 

 (Equal to about 37.8 square feet. 



Having made this arrangement,! found the temperature of the apart- 

 ment which had, in former years, required a separate grate, or stove, 

 to keep it in a comfortable condition, entirely freed from that neces- 

 sity, and during the whole season, which will long be remembered 

 as one of uncommon severity, not a single hour is known to have 

 found it untenantable from cold. At night, the fire in the kitchen 

 was prepared for a slow operation, by adding a fresh supply of coal 

 covered closely by a layer of the finer kind called " chestnut coal" 

 or, what is still better, the coarser parts of the sifted cinders from 

 which the earthy and vitrified portions were always carefully rejected. 

 In this state of the fire, the temperature of the entering gas was con- 

 siderably reduced, but in no instance was it found lower than 100°. 

 It is probable that the mass of brick work, constituting the chimney 

 having become hot during the day, contributed to keep up the tem- 

 perature in the drum during the night, — a contribution which would 

 have been utterly wasted on the " upper air" according to the usual 

 method of arranging both wood fires and open grates. 



In the following table are given the results of numerous observa- 

 tions made, some at irregular intervals during the winter, others at 

 regular periods of five or ten minutes apart, continued for several 

 hours in immediate succession. They are arranged according to 

 the temperature of the entering gas which, it will be observed, was 

 never higher at the time of any observation, than 231°. The chan- 

 ges were, in general, so gradual as to allow a perfect facility in noting 



