Nitrogen  and  Oxygen  and  of  Argon  and  Oxygen.       655 
Table  X. 
Benzene  and  Acetic  Acid.     49°* 99  C. 
No. 
Concen- 
tration 
of 
Pressure. 
Concen. 
Press. 
Molec. 
Weight 
of  Acetic 
Acid  in 
Concen- 
tration 
of  Acetic 
Pressure. 
Concen. 
Press. 
Benzene, 
Acid. 
Vapour. 
1  ... 
84-5 
(268-9) 
(•314) 
0 
0 
2 
83-3 
2623 
•318 
83-0 
1-44 
3-63 
•397 
3  '.'.'. 
816 
258-7 
•316 
89-1 
3-51 
6-53 
•539 
4  ... 
81-0 
257-2 
•315 
90-1 
430 
7-25 
•593 
5  ... 
77"4 
249-6 
•310 
94-7 
8-56 
11-5 
•745 
6  ... 
74-6 
244-8 
•305 
974 
11-92 
14-2 
•839 
7  ... 
69-3 
231-8 
•299 
99-3 
18-3 
18-4 
•994 
8  ... 
65-9 
224-7 
•294 
100-4 
22-4 
20-5 
1-092 
9  ... 
57-9 
211-2 
•274 
102-0 
32-1 
24-8 
1-29 
10  ... 
53-3 
200-9 
•265 
102-5 
37-6 
27-1 
1-39 
11  ... 
514 
195-6 
•263 
103-1 
39-8 
28-7 
1-39 
12  ... 
33-0 
1532 
•215 
104-8 
621 
36-3 
1-71 
18  ... 
30-6 
147-2 
•208 
105-0 
65-0 
36-8 
1-77 
14  ... 
26-6 
135-1 
•197 
105-4 
69-8 
40-2 
1-74 
15  ... 
11-8 
75-3 
•157 
107-0 
87-5 
50-7 
1-73 
16  ... 
1-5 
18-3 
•114 
107-9 
999 
54-7 
1-83 
17  ... 
0-5 
3-5 
•148 
107-9 
101-1 
54-7 
1-85 
18  ... 
0 
0 
101-7 
(56-5) 
(1-80) 
been  calculated  from  the  densities  of  the  two  components 
assuming  that  no  contraction  takes  place  on  mixing.  Until  the 
densities  of  these  mixtures  have  been  determined,  a  close 
relation  between  the  calculated  concentrations  and  the 
pressures  cannot  be  looked  for.  It  is  possible  that  this 
explains  the  fact  that  in  Tables  IX.  and  X.  the  quotient  for 
benzene  rises  with  the  concentration,  whereas  in  Table  VII. 
the  quotient  falls. 
But  the  case  of  the  distillation  of  acetic  acid  and  benzene, 
the  results  of  which  are  given  in  Table  X.,  is  particularly 
interesting  from  the  point  of  view  of  agreement  with  Henry's 
law.  Acetic-acid  vapour  has  a  molecular  weight  which  shows 
that  the  vapour  consists  of  a  mixture  of  simple  and  double 
molecules.  Now  when  acetic  acid  is  dissolved  in  benzene, 
even  in  the  most  dilute  solutions,  the  acetic  acid  consists 
entirely  of  double  molecules.  Hence,  when  acetic -acid 
vapour  dissolves  in  benzene,  association  takes  place,  and  this 
ought  to  be  shown  if  the  partial  pressure  be  plotted  against 
the  concentration.  From  Table  X.  it  will  be  seen  that 
neither  the  partial  pressure  of  the  acetic  acid  nor  that  of 
the  benzene  is  proportional  to  the  concentration,  and  that  the 
association  factor  in  the  case  of  acetic  acid  is  considerable. 
