582 
DR. ANDREWS ON THE CONTINUITY OE THE 
were made, indicated an increase of pressure of about one-fourth of an atmosphere (from 
48*89 to 49*15 atmospheres) during the condensation of the first and second thirds of 
the carbonic acid. According to theory no change of volume ought to have occurred. 
This apparent anomaly is explained by the presence of the trace of air (about -g-^ 
part) in the carbonic acid to which I before referred. It is easy to see that the increase 
of pressure shown in these experiments is explained by the presence of this small quan- 
tity of air. If a given volume of carbonic acid contain -g-^ of air, that air will be 
diffused through a space 500 times greater than if the same quantity of air were in a 
separate state. Compress the mixture till 50 atmospheres of pressure have been applied, 
and the air will now occupy, or be diffused through, ten times the space it would occupy 
if alone and under the pressure of one atmosphere ; or it will be diffused through the 
space it would occupy, if alone and under the pressure of ^ of an atmosphere. 
While the carbonic acid is liquefying, pressure must be applied in order to condense 
this air ; and to reduce it to one-half its volume, an increase of of an atmosphere 
is required. The actual results obtained by experiment approximate to this calcula- 
tion. From similar considerations, it follows that if a mixture of air and carbonic acid 
be taken, for example in equal volumes, the pressure, after liquefaction has begun, must 
be augmented by several atmospheres, in order to liquefy the whole of the carbonic acid. 
Direct experiments have shown this conclusion to be true. 
The small quantity of air in the carbonic acid disturbed the liquefaction in a marked 
manner, when nearly the whole of the carbonic acid was liquefied, and when its volume 
relatively to that of the uncondensed carbonic acid was considerable. It resisted for 
some time absorption by the liquid, but on raising the pressure to 50*4 atmospheres it 
was entirely absorbed. If the carbonic acid had been absolutely pure, the part of the 
curve for 13°T (figure, page 583) representing the fall from the gaseous to the liquid 
state, would doubtless have been straight throughout its entire course, and parallel to 
the lines of equal pressure. 
Table II. — Carbonic Acid at 21°*5. 
s. 
t . 
s- 
t \ 
l . 
1 
4670 
8-63 
1 
67*26 
21*46 
272*9 
1 
60*05 
8*70 
1 
114*7 
21*46 
160*0 
1 
60*29 
8-70 
1 
174*8 
21*46 
105*0 
1 
60*55 
8*70 
1 
240*5 
21*46 
76*3 
1 
6roo 
8-70 
1 
367*7 
21*46 
49*9 
62*21 
8-70 
1 
440*0 
21*46 
41*7 
1 
6*2*50 
8*70 
1 
443*3 
21*46 
41*4 
