288 
MR. C. T. R. WILSON ON CONDENSATION OF WATER VAPOUR 
Expansion required to produce the Sensitive Tint. 
Date. 
B. 
1 
O 
Q 
Pi- 
Pr 
Pr 
P- 
Pj Po— 
Colour. 
March 6 
752 
19-5 
17 
804 
1538 
347 
1081 
1-423 
Violet 
„ 7 . . 
775 
17 5 
15 
799 
1558 
341 
1100 
1-417 
Mean 
1-4-20 
1 
Carbonic Acid. 
Preparation .—Potassium bicarbonate was heated in a glass tube, fused directly 
to H. This was repeatedly heated and pumped out, 
Residts .—Clarbonic acid shows, like air and oxygen, the two kinds of condensation, 
each requiring a definite minimum expansion for its production. 
The measurements could not be made with the same accuracy in this case on 
account of the solubility of the gas in water. This caused a continual falling off in 
the pressure, necessitating the reading of the final pressure p^ after each expansion. 
On account of the difference in y, the results with COo are not directly comparable 
with those obtained with air, the same expansion corresponding to a different fall of 
temperature. 
The colour phenomena were not looked for. 
In the table which follows, the pressure readings corresponding to the greatest 
expansion which was made without condensation, as well as those of the least 
expansion which resulted in condensation, are given. In the case of the more 
insoluble gases, the difference between these only amounted to 2 millims. ; here, as 
will be seen, it is considerably greater. 
Rain-like Condensation in CO3. 
Date. 
B 
f C. 
"iT» 
P\- 
Pi- 
Pr 
Po- 
Pi'Po- 
1 
Result. 
May 23. 
764 
19 
16 
710 
1457 
333 
1080 
1-349 
0 
>5 . 
764 
19 
16 
700 
1447 
314 
1061 
1-364 
Rain 
May 25. 
775 
17 
14 
605 
1355 
247 
997 
1 -359 
0 
99 ..... 
775 
17 
14 
612 
1362 
245 
995 
1-369 
Rain 
May 25. 
775 
17 
14 
599 
1349 
242 
992 
1-360 
0 
99 . 
775 
17 
14 
603 
1353 
240 
990 
1-367 
Rain j 
Condensation begins when Pj/Pg is between 1*36 and 1’37. 
For pressure changes within these limits (between and 2 atmospheres) Boyle’s 
