F 



Properties of a Mixture of Liquids. 



409 



the pressure in this way the liquid boiled gently, and in a 

 minute or two enough had collected in the receiver to be 

 withdrawn for analysis, i. e. about 2 cub. centim. The opera- 

 tion was repeated three or four times on the same mixture, 

 without removing it from the flask, and analyses made of the 

 distilland before and after the whole experiment. 



The method of analysis that enabled me to use such small 

 quantities of liquid, and at the same time to work very expe- 

 ditiously, consisted in determining the refractive index by a 

 Pulfrich refractometer. This instrument — of the usual type 

 — was of sensitiveness enough to give the refractive index to 

 about *00005 (corresponding to about half a minute in the 

 angle reading). Now, for benzene yu, = l*50, while for the two 

 esters it is about 1*37 ; hence a change of composition of y 1 ^ 

 per cent, would cause a change in the refractive index of 

 •00013, and could quite well be detected. To attain that 

 degree of accuracy it was necessary to know the temperature 

 to about -^ degree ; as the temperature-coefficient is '00052 

 to '00065 per degree. The measurements were carried out 

 in a room that rarely differed by one degree from 18°, and it 

 was therefore thought sufficient to interpolate the temperature 

 coefficients of the mixtures from those of the pure substances 

 given in Landolt and Bornstein's tables, and reduce all the 

 observations to that temperature. 



The preliminary measurements of the refractive index of 

 the mixtures weighed out for the purpose, gave the following 

 results : — 



Benzene and Ethyl Acetate. 



Per cent. 



Temp, of 



of benzene 



experi- 



by weight. 



ment. 







o 



176 



13-88 



16-1 



27-92 



160 



44-67 



16-0 



5585 



15-4 



69-40 



16-4 



86-76 



16-4 



100 



17-8 



fi (obs.) 

 reduced to 



18°. 



1-37326 

 1-39095 

 1-40870 

 1-42991 

 1-44424 

 1-46219 

 1-48501 

 1-50238 



(additive). 



1-39117 

 1-40931 

 1-43093 

 1-44537 



1-46287 

 1-48529 



(calc). 



1-39069 

 1-40850 

 1-42994 

 1-44438 

 146203 

 1-48482 



/^calc. /^obs. 



- -00026 

 - 20 



+ 

 + 



3 

 14 

 16 

 19 



The fourth column gives the values of //, calculated on the 

 supposition that it is a strictly additive property, i. e., 



= 1-37326 (l-a>) +1-50238 a?, 

 where a is the fractional amount of benzene present. The 



