60 Chemical and Physical Notes 



the cryohydric temperature and concentration have been 

 reached. The temperature of the boiling solution remains 

 constant, and steam and salt quit it part passn. In the 

 freezing solution the salt and ice are both solid, and remain 

 associated in the cryohydrate. In the boiling solution the 

 salt is solid and the steam is gaseous, and they part company 

 of themselves. 



The fact that steam produced by water boiling at 100 C, 

 which under ordinary circumstances can produce by its con- 

 densation no higher temperature than that at which it was 

 generated, should be able to raise the temperature of saline 

 solutions many degrees above this temperature, appears at 

 first sight paradoxical, and it was, in fact, largely disbelieved, 

 in spite of the simplicity of the experiment to demonstrate it. 



In a paper already referred to, the use of ice melting in 

 saline solutions of definite nature and strength was strongly 

 recommended as affording an absolute thermometric scale for 

 such temperatures. Extending these researches to steam and 

 brines, the writer found that the condensation of steam in 

 saline solutions could be used for fixing, or verifying, tempera- 

 tures above the boiling-point of water. Also steam, water and 

 salt can be used to form boiling mixtures, exactly as ice, water, 

 and salt are used to form freezing mixtures ; and an inde- 

 pendent and absolute thermometric scale is produced for 

 high temperatures, just as with ice we have one for low 

 temperatures. 



These melting and condensing temperatures are intended 

 to give fixed points of reference on the thermometer below 

 the ordinary freezing- and above the ordinary boiling-point, 

 and they can be chosen to suit the work in hand. Thus, if 

 work is being done where temperatures about 108 or 109 C. 

 are to be measured with the accuracy which is demanded of 

 a thermometer on which the Centigrade degree occupies 

 a length of one or perhaps two centimetres, it is not sufficient 

 to verify the ordinary boiling-point, because the part of the 

 scale of the thermometer used may be ten or fifteen centi- 

 metres distant from it, and to verify the scale by careful 

 calibration entails great labour. It is, however, very simple 



