74 Mr. N. D. C. Hodges on the Size of Molecules. 



for any number of faults and for all the terminal arrangements 

 that can be made out of those shown in fig. 4. The denomi- 

 nator of (19) is a function of a t and b t . Thus 



A,- 5^ (*9 



[To be continued.] 



VIII. On the Size of Molecules. By N. D. C. Hodges*. 



IF we consider unit mass of water, the expenditure on it of 

 an amount of energy equivalent to 636*7 units of heat 

 will convert it from water at zero into steam at 100°. I am 

 going to consider this conversion into steam as a breaking-up 

 of the water into a large number of small parts, the total sur- 

 face of which will be much greater than that of the water 

 originally. To increase the surface of a quantity of water by 

 one square centimetre requires the use of '000825 metre- 

 gramme of work. The total superficial area of all the parts, 

 supposing them spherical, will be 4-7T r 2 N, the number of parts 

 being N. The work done in dividing the water will be 47r 

 r 2 N '000825. For the volume of all the parts we have |7r 

 r 3 N. This volume is, in accordance with the requirements of 

 the kinetic theory of gases, about 30*00 of the total volume 

 of the steam. The volume of the steam is 1752 times the 

 original unit volume of water. Hence — 



f<7n< 3 N 3000 = 1752 



4tt»« 2 N -000825 = 636-7423 



One unit of heat equals 423 units of work. 



Solving these equations for r and N, we get r = -000000005 

 centimetre, a quantity closely corresponding with the previous 

 results of Sir William Thomson, Maxwell, and others ; and ISP 

 equal 9000 (million) 3 , or for the number in one cubic centi- 

 metre 5 to 6 (million) 3 . 



Around every body there is an atmosphere of more or less 

 condensed gases. On the surface of platinum these must be 

 nearly in the liquid condition, as shown by the power of plati- 

 num to bring the atoms of oxygen and hydrogen so near 

 together that they combine. These vapours on the surface 

 have a tendency at ordinary temperatures to expand; and part 

 of them can do so, if the surface of the body is reduced. There 

 is in these condensed atmospheres an explanation of all the 

 phenomena of superficial tension. The energy in the unit of 

 area ought to be equal to the work done in compressing a 

 * Communicated by the Author. 



