312 Experimental Inquiries respecting Heat and Vapor. 



To place the matter beyond a doubt, the iron basin already men- 

 tioned was used. When exposed to the white heat of a forge fire, 

 a given weight (one eighth of an ounce) of water was evaporated in 

 sixty seconds. At the bright red heait of an anthracite stove, eighty 

 seconds were required to produce the same effect. When exposed 

 on an open grate of anthracite, in such a manner as to maintain the 

 centre only of the basin at a very faint red heat in the dark, the time 

 was extended to three hundred and fifteen seconds. 



Another comparison, made upon portions of water of one sixteenth 

 of an ounce each, gave the following results. On the metal, at the 

 bright red heat of the stove, the water lay sixty six seconds ; on the 

 centre of the basin dull red, as before, in the dark, it continued one 

 hundred and eighty three seconds; while over a spirit lamp, the metal 

 being constantly black and the temperature probably not above 600°, 

 it remained two hundred and eighty six seconds. 



In all the above experiments, the heat was constantly supplied, and 

 the temperature may be regarded as having been uniform during each 

 trial. Hence, the opinion that repulsion increases with the tempera- 

 ture, appears not to be sustained. When the temperature has deci- 

 dedly surpassed the point where contiguous attraction can take place, 

 every elevation of temperature is attended with a corresponding dimi- 

 nution of time required for evaporation. 



In order to illustrate more fully this branch of the subject, a series 

 of experiments was made with the iron basin, placed over a coal fire 

 and supplied with doses of one sixteenth of an ounce of alcohol, sp. 

 gr. .854, (32.5° Baume.) The first experiment was made at a 

 temperature about 400° to 500°. 



The following was the succession. 

 Exp. 1 - - 142'' Exp. 3 - - 140'^ 



2 - - - 145 4 - - - 117 



The temperature of the metal continued to rise notwithstanding the 

 application of the successive portions of spirit, and as the time for 

 each experiment was obviously decreasing through an excess of tem- 

 perature, the basin was removed from the fire and allowed to stand 

 for some time, until it was cooled below the point of minimum activity. 

 It was then again placed upon the fire, and when the fifth portion of 

 liquid was placed upon it, exhibited symptoms of a slight tendency 

 to attract the latter. The sixth experiment was made after sufficient 

 time had elapsed again to permit a rise of .temperature. 



