Freezing-points of Solutions of Water in Formic Acid. 11 



means of Beckmann's apparatus on a mercury thermometer 

 (J. Hicks, London) divided in ^q°, corrections of which were 

 given by the Kew Observatory. 



Solutions of water in formic acid were prepared in a glass 

 bottle (of 50 c. c.) with a glass stopper, by weighing the 

 bottle, then the bottle and the acid, and finally weighing the 

 whole, when some drops of water had been very carefully 

 added. 



I first tested whether the formic acid, which is very hygro- 

 scopic and easily decomposes, remained in a constant state 

 for the time (some hours) during which the observations of 

 the resistances and freezing-points were taken. The best way 

 to test this is, of course, by the measurement of the resistance 

 of the acid during some days. 



The following table (Table I.) shows three such observations 

 for three different solutions, freezing at 7*69, 5*4:6, 5*38 

 respectively : — 



Every measurement started with a solution, which was 

 prepared by freezing; the second solution (5*46 f.-p.) was 

 left in the resistance-cell for the whole time (145 hours) ; 

 the others were put immediately in the bottle after the 

 measurement. 



The conductivity increases during the time, more rapidly 

 the first day than afterwards, showing that the acid takes 

 some water from the air or that it decomposes slightly, 

 especially if in contact with platinum black on the elec- 

 trodes. 



More concentrated acid seems to be more hygroscopic 

 than dilute acid — the observations show that it is as difficult 

 to keep the concentrated acid unchanged as to prepare it. 

 It follows clearly that all the measurements referring to one 

 solution must be made in a very short time, and that it is not 

 possible to get a high accuracy in results. 



Every solution was measured at four or five different tem- 

 peratures, beginning from a temperature near the freezing- 

 point and repeating the reading at each temperature four 

 times at equal intervals so as to be sure that the temperatures 

 of the solution and of the bath were the same. 



Every solution was prepared from the fresh, most concen- 

 trated, acid, or from acid which had been distilled and frozen 

 just before it was used for the measurements. All this 

 treatment took up a great deal of time, because the greatest 

 care was spent in preparing the acid pure. 



Table II. shows the results. In the first column are freezing- 

 points (F. P.), in the second the specific conductivity in 

 terms of mercury at 0° (c . 10 9 ), in the third the temperature of 



