Ice and its Natural History 245 



the principle to the discussion of the apparent variations of 

 volume of a block of ice, the volume of which at o C. is 

 1000 c.c. It contains diffused through it 1*5105 gram NaCl, 

 which we assume to be provisionally in the inert state, in 

 which it is deprived of the power to induce the melting of 

 ice at temperatures between oC. and -2i72C. Let the 

 temperature of the block containing the inert NaCl be reduced 

 to 23 C. ; its volume will be reduced to 996^320 c.c., and as 

 the temperature is below the cryohydric temperature, the salt 

 is by nature inert ; at such temperatures ice and common 

 salt are indifferent to each other. Let the temperature of 

 the block of ice be now raised to 22; the salt remains 

 inert, and the volume of the ice increases to 996*48 c.c. If 

 the temperature is further increased to 2i*72i, the NaCl 

 will still remain inert, and the volume of the ice will become 

 996-525 c.c. 



If the heating is continued the temperature rises exactly 

 to the cryohydric point, 21 72, at which temperature the 

 indifference of chloride of sodium to ice ceases, and induced 

 melting at that temperature takes place. It will then be 

 observed that the temperature remains constant for a time, 

 while the volume of the block diminishes. When the tem- 

 perature begins to rise, the volume of ice melted will be 

 5 '498 c.c. As this produces 5*040 c.c. water, the diminution 

 of volume is 0-458 c.c, and the apparent volume of the block 

 is 996-067 c.c. 



Let us now go back to the initial state, in which we have 

 the block of loooc.c. ice, containing 1-5105 gram inert NaCl 

 diffused through it, at the temperature o C. Let the tempe- 

 rature be reduced to 2iC, the ice remaining inert. The 

 volume of the ice will then be 996-64 c.c. Let the NaCl 

 recover its activity, it will melt 5*629 c.c. ice, producing 

 5-160 c.c. water under a contraction of 0-469 c.c., so that the 

 apparent volume of the ice at 2iC. is 



99664 - 0-469 = 996*171 c.c. 



By the aid of Table I and the other constants we can 

 calculate the composition of a block of ice of any weight or 



