252 Ice and its Natural History 



In his work on The Properties of Water and Ice, Pettersson 

 gives in Plate XXI the. curves of the change of volume with 

 temperature, of three samples of ice frozen from samples of 

 melted sea-ice. They are numbered in descending order 

 of concentration, VI, V and IV. For the details, which are 

 interesting, the reader must consult the original work. The 

 nature of these samples is roughly indicated by their specific 

 gravity at o C., referred to that of distilled water at 4 C, and 

 by the percentage of chlorine in them. 



I calculated by the method which I have above developed, 

 the volume of ice at o, containing i'5iO5 gram chloride of 

 sodium, which would show the same volumetric behaviour as 

 these samples. The results are given in Table IV. 



Pettersson's volumes (P) for certain whole degrees of 

 temperature (?) are taken. The water which agreed with 

 the volumetric behaviour of each of Pettersson's samples 

 was found empirically, and the volume of the ice at each 

 temperature, t, for each sample calculated as in Table II. 

 The temperature, /, at which Pettersson observed the volume 

 to be a maximum was the chief guide. The volumes obtained 

 by my method are found in line U. I then took my volume 

 and Pettersson's volume for the temperature at or near the 

 maximum of volume, and obtained a factor by which I re- 

 duced my volumes at the other temperatures to the same 

 denomination as those of Pettersson. These are given in 

 line B, those of Pettersson being given in line P. It will 

 be seen that the agreement between calculation and ob- 

 servation is very good. 



Cryoscopic Equivalence between Pressure and Salinity. 

 We have seen that the freezing-point of water and melting- 

 point of ice is lowered by increase of pressure and by addition 

 of salt in solution. The effect produced by these agencies is 

 the same in kind. 



