of Water from Salt- Solutions, 505 



In my experiments 1 had two methods available ; either the 

 barometer-tube method as modified by Konowalow, or the 

 boiling-point method modified so that the temperature was 

 constant and the pressure the variant. The latter is by far 

 the more convenient of the two methods, and is the one that I 

 employed; but it was only after repeated trials that I succeeded 

 in overcoming the danger of superheating and the conse- 

 quent error of experiment. 



A flask, about 200 cubic centim. capacity, communicates by 

 a wide side- tube with an upright condenser ; this in its turn is 

 connected with a three-way tap and an air-reservoir, w T hich 

 communicates with the gauge and the water-pump. The 

 flask stands on a small burner, and is protected from the heat 

 by a metal ring, except about an inch and a half at the very 

 bottom. In the neck of the flask is fitted the thermometer. 

 The course of experiment was as follows : — In the flask was 

 placed 50 grammes of zinc and 60 cubic centim. of water, 

 then ^ of the molecular weight of the salt in grammes were 

 added. This gives a solution of almost exact molecular 

 strength, as y|g- - = Jq- The thermometer was introduced, 

 care being taken that the bulb was completely immersed ; the 

 side-tube joined to the condenser, the pump set in action, 

 and the burner lighted. When the solution boiled, the pres- 

 sure was slowly increased till the thermometer rose to 70° O. 

 The barometer and gauge were then read by two telescopes, 

 the pressure was again diminished slightly, a tube full of 

 mercury introduced into the reservoir of the barometer, and 

 another reading made at 70°, the mean of the two being 

 taken. The same operations were repeated at intervals of 

 5° G. up to 95° C, when the flask was disconnected, washed, 

 and dried, and the whole set of observations repeated with a 

 fresh solution of the same strength. Thus each determination 

 given in the following Tables is the mean of four results, ob- 

 tained with two separately prepared solutions. The granulated 

 zinc is absolutely necessary in large quantity, otherwise super- 

 heating takes place. In no case was the zinc dissolved by the 

 solution ; nor was it appreciably attacked, except by the very 

 strongest solutions of KN0 3 and NaN0 3 at the higher tempe- 

 ratures. In these cases appreciable amounts of ammonia 

 were evolved, a point I intend to investigate further ; but 

 even after prolonged boiling the boiling- pressure was found 

 unaltered ; thus the results are not affected by the small de- 

 composition of the salt in these cases. The remainder of the 

 method of experiment is the same as that described in my 

 previous paper. It must not be forgotten that, though the 

 temperatures are arbitrary, still, as the determinations were 



