Chemical and Physical Notes 61 



to expose the thermometer in a vessel of the form about to 

 be described to the action of steam condensing in a mixture 

 of common salt and brine, which gives a perfectly fixed 

 temperature at a given barometric pressure. And these 

 conditions can be reproduced at any future time, and the 

 readings of the thermometer in the immediate neighbourhood 

 of this fixed temperature can thus be verified as accurately 

 as if they had been as near to the ordinary boiling-point of 

 distilled water. 



For temperatures above the boiling-point of water it is 

 convenient to use " boiling mixtures," where the dry salt is 

 put in a suitable vessel holding a thermometer, and the steam 

 is blown through it until the bulb of the thermometer is im- 

 mersed in a boiling mixture of brine and solid salt, and the 

 stem is immersed in its steam. 



One of the most convenient salts for this purpose is 

 chloride of sodium, on account of its almost uniform solubility 

 at different temperatures. At ordinary atmospheric pressure 

 it raises the condensing point of steam by 8'4 C., or I5'i F. 

 If a weighed quantity of salt has been used and the apparatus 

 has been also weighed, then by continuing to blow in steam 

 after all the salt has been dissolved, and weighing the 

 apparatus when the temperature has fallen to certain definite 

 degrees, a series is obtained of the temperatures at which 

 steam condenses in solutions containing definite amounts of 

 salt. This has been done for a number of salts. It is a much 

 more accurate way of determining the boiling-point of a 

 solution than by boiling it over a lamp flame. This holds 

 generally. To determine the boiling-point of a liquid it should 

 be boiled by its own steam, 



The apparatus used is shown with the boiling flask and 

 lamp in Fig. 2. The steam tube is U-shaped ; the one leg 

 has a large body, CB, 15 cm. long and 4 cm. wide. This is 

 continued upwards in the tube A C, which is 1 5 cm. long and 

 12 mm. wide. The exit tube D has an internal diameter of 

 7 mm., and the entry tube E has also 7 mm. diameter, or 

 slightly less. The dry salt is introduced into CB ; the ther- 

 mometer passes through a cork at A, and the bulb is covered 



