MATTER 19 



of a centimetre, or about */&, 500,000 of an inch, if water 

 is not porous. 



In a similar way for solids — taking ammonium 

 nitrate, N Hj N Oa, for example, one cubic centi- 

 metre of which contains 2,083 cubic centimetres of its 

 three constituent gases, the number of molecules in 

 1 c. c. of the solid would be 39,577,000,000,000,000,- 

 000,000, and the average diameter of the molecule, if 

 the solid is not porous, would be V34,ooo,ooo of a cen- 

 timetre in diameter, or about V85,ooo,ooo of an inch. 



Taking another solid, ammonium bicarbonate, N H4 

 H C O3, we estimate the size of the molecules of its 

 elements to be about 1 /u,m,(m of a centimetre, or 

 about Y86,25o,ooo of an inch. In this estimate the 

 substances were taken in the simple form and the 

 carbon was assumed to occupy the same space that it 

 would occupy if it had the specific gravity of the 

 diamond. 



Instead of the above method, we may regard the 

 N H4 H C O3 as being composed of the two gases 

 N H3 and C O2 and of water, H2 O. The average 

 size of the molecules of these three compounds is 

 about Y29,5oo,ooo centimetre, or 1 /w,m,ow of an inch. 



The above estimates of the sizes of molecules, as 

 already stated, are made upon the assumption that 

 solids and liquids are not porous, or that there are no 

 vacant spaces between the molecules. 



That there are such spaces, however, is evident 

 from the fact that both solids and liquids can be com- 

 pressed into smaller volumes than they occupy at 

 O C, and from the fact that they contain heat, which 

 forces the molecules apart. 



I think, however, that the vacant spaces between 

 the molecules of a solid are small compared to the 

 space occupied by the molecules themselves. 



It seems probable that at the absolute zero, namely, 



