CHEMICAL AND PHYSICAL NOTES. 105 
boiling mixture of steam and NaCl under the barometric pressure 
(P) ; under p ( = 1-345 P), the calculated tension of saturated steam 
of temperature ¢; and under t—Z, the excess of boiling-point of 
saturated NaCl solution above that of pure water under the given 
pressure. This table gives figures which agree closely with the 
results of the writer's observations in Switzerland at nine different 
altitudes, varying from 400 to 2773 metres. It appears that the 
alteration in the solubility of NaCl between the temperatures 91° C. 
and 100°C. is so slight that the relative depression of vapour tension 
is not sensibly affected. 
The practical value of these results is that, if a thermometer be 
exposed to the action of pure saturated steam, and to a boiling 
mixture of steam and NaCl, and the temperature noted in each case, 
the difference of these temperatures, compared with the tabular 
value of t—Z' for the existing barometric pressure, furnishes a direct 
and easily applied control of the graduation of the thermometer over 
the observed range. 
TaBLe VIII.—Givine THE BaromETric PREssURE aT WHICH A BorLinc MIxTORE oF 
Srzam AND CHLORIDE OF SopIUM HAS A CERTAIN TEMPERATURE; the Limits of 
Temperature being 109° and 99° C. 
tee of ee Kiareepondiee to gies re of) Barometric dotiedpondine to 
Mixture. essure. a a of Mixture. Pressure. a ai of 
t P ap t P dp 
° ° 
109 T73°4 ae 104 650°9 Se 
108°5 760°2 2°60 103°5 639°8 2°22 
108 T47T°4 2°40 103 628°7 2°22 
107°5 734°9 2°50 102°5 617°8 2°18 
107 722°4 2°50 102 607°0 2°16 
106°5 710°2 2°44 101°5 596°3 2°14 
106 698-0 2°44 101 585°7 2°12 
105°5 686°1 2°38 100°5 575°3 2°08 
105 674°2 2°38 100 565°1 2°04 
104°5 662°5 2°34 90°5 555°1 2°00 
104 650°9 2°32 99 545°1 2°00 
For information about other salts in this respect, the reader is 
referred to the writer’s paper on ‘ Steam and Brines.’ 
Before passing from this subject attention may be directed to the 
following interesting connection between the freezing and the boiling 
of saline solutions. 
