304 Experimental Inquiries respecting Heat and Vapor. 



Art. VIII. — Experimental Inquiries respecting Heat and Vapor, 

 with some practical applications ; by Walter R. Johnson, Pro- 

 fessor of Mechanics and Natural Philosophy in the Franklin Insti- 

 tute, Philadelphia. 



The developement of the law of action between a heated surface 

 and water of different temperatures, has been, in part, presented by 

 preceding courses of experiments. 



To persons conversant with this subject it will readily occur, that 

 the facts and principles connected with vaporization are highly im- 

 portant to the arts, independently of their relation to the steam en- 

 gine. The numerous processes of manufactures, in which liquids 

 are to be reduced by boiling, are often performed in a manner totally 

 at variance with philosophy, as well as with economy. The manu- 

 facture of salt by vaporization, for example, is an extensive and in- 

 creasing branch of our national industry, and is generally carried on 

 with very little attention to the saving of fuel, by any of those devices 

 and arrangements which the practical science of the present age 

 might suggest. 



The chief points proposed to be examined at present, are — 



1. The temperature of inost rapid vaporization under atmospheric 

 pressure. 



2. The nature of the phenomena exhibited at that point, as well 

 as immediately above and below it. 



3. Effects of lubricating the surface of the metal, of covering the 

 surface of the water with a thin fibrous texture, and of thickening it 

 with a farinaceous substance. 



4. The influence of mechanical pressure in bringing the liquid in 

 contact with the metal and accelerating the vaporization. 



5. The action of hot metal on other liquids, particularly alcohol. 



6. Some opinions which have gained currency in regard to the 

 temperature of repulsion, and the degree of rapidity with which heat 

 may be imparted to liquids, will likewise require attention. 



1. To ascertain the temperature at which the most rapid action 

 takes place, two methods have been employed. The first was by 

 using a basin of wrought iron, having at the bottom a small quantity 

 of mercury, into which the bulb of a thermometer was plunged. 

 Upon the surface of the iron, near the mercury, small measured por- 

 tions of water were successively deposited, while the basin was pla- 



