254 fee and its Natural History 



On the same grounds it seems to be legitimate to say 

 that the salt in solution acts also by influence ; and its 

 influence is subject to quantitative law which has been well 

 investigated. 



As both influences are subject to known laws, we are able 

 to ascertain the equivalence which exists between them. 



Further, the pressure, being immaterial, is of one kind, 

 while the salt, which is material, is of as many kinds as there 

 are chemically individual substances soluble in water. 



In considering the two agencies, we must compare a 

 certain absolute pressure with a certain weight of a parti- 

 cular salt. In this discourse we have generally considered 

 the constant quantity I'51O5 gram chloride of sodium. The 

 generally accepted pressure which lowers the freezing-point 

 of water by iC. is 135 atmospheres, which is here taken as 

 equivalent to 140 kilograms per square centimetre (kg./cm. 2 ). 

 If we consider the surface of the water which is exposed to 

 the pressure as 100 square centimetres, then the total pressure 

 required is 14,000 kg. We therefore take as our constant 

 absolute pressure 14,000 kg. When the distilled water ex- 

 poses to it a surface of 100 cm. 2 its freezing temperature is 

 lowered by i C. If the lowering of the freezing-point of 

 water by pressure were simply proportional to the pressure, 

 then, when the surface exposed to the pressure of 14,000 kg. 

 is s cm. 2 , the lowering of the freezing-point would be given 

 by / in Table V. It results, however, from the experiments 

 of Tammann 1 that proportionality of the lowering of the 

 freezing-point of water to the pressure to which it is ex- 

 posed, is of the same order as that of the lowering of the 

 freezing-point of water to the amount of salt dissolved in it. 

 In Table V, / gives the surface (cm. 2 ) of water which must be 

 exposed to a pressure of 14,000 kg. in order that, according 

 to Tammann, its freezing-point may be lowered by t degrees. 

 The corresponding volumes of ice melted, at ordinary pressure, 

 under the influence of i"SiO5 gram NaCl, are given by v. To 

 be strictly comparable with s and s', the numbers v should be 



1 ' Ueber die Grenzen des festen Zustandes,' von G. Tammann, Annalen der 

 Physik, [ 4 ], ii. i. 



