Volume Changes attending Mixture. 499 



Another resource would be of course to measure the degree 

 of separation approximately by measuring the height of the 

 plane of separation of the two immiscible mixed liquids heated 

 by a known mass cooling through a known range. This 

 would be indeed in theory a very effective calorimeter; but I 

 do not see the way at present to overcome certain practical 

 difficulties of arrangement and manipulation. 



§ 258. Diethylamine and Water. — These two liquids appear 

 to mix in all proportions at all atmospheric temperatures 

 above 0° C. An aqueous solution of the base, when heated 

 in an open vessel, gives off the base as a vapour, and the 

 temperature does not rise above 100° C. 



Into a strong glass tube, which was afterwards sealed, was 

 introduced a mixture consisting of 45 '42 per cent, of diethyl- 

 amine and 54'58 per cent, of water. On heating this in an 

 oil-bath, with a thermometer, very gradually, and again letting 

 the temperature fall slowly, the bath being kept well stirred, 

 the following changes were observed : — 



At 1 30° the liquid was still quite clear. 

 134°' 5 separation was incipient. 

 135°. The lower layer amounted to about \ of the whole. 



1 3fi° i 



±ov • v •>•> •>•> 4 It 



140° 2 



14-5° i 



1 ^0° -I 



^ ayj ' )■) 11 JJ 3 V 



" " " " 3 v 



The conditions were not such as to allow of exact measure- 

 ment. The critical temperature is, however, trustworthy ; 

 and the result shows that, within a range of about 10° C. only, 

 the separation begins and is completed, as far as the com- 

 pletion is faithfully measured by the height of the plane of 

 demarcation. It is to be noted that, owing in part to the re- 

 fractive index of diethylamine being nearer that of water 

 than is the refractive index of triethylamine, the above sepa- 

 ration is not marked by the milkiness which characterizes the 

 separation of the latter body *. If it were not for accidental 

 dust-particles floating on the surface of the lower liquid it 

 would be, in some cases, almost impossible to distinguish the 

 two layers. As the phenomenon of separation is one which 



* Mr. Illingworth, a student in my physical laboratory, ha^ been kind 

 enough to determine the refractive indices of this group. 



P 

 Ethylamine .... 1'3718 

 Diethylamine. . . . 1*3850 

 Triethylamine . . 1 -31-99 

 The determinations were made at 17° O., a temperature rather perilously 

 near the boiling-point of ethylamine. 



