| Hydrogen in | 57″ |
| Olefiant gas in | 135″·5; |
but equal volumes of each passed through the same tube at equal low pressures in the following times:—
| Hydrogen in | 8′ 15″ |
| Olefiant gas in | 8′ 11″. |
Again, equal volumes of carbonic oxide and carbonic acid gases passed at equal high pressures through the same tube,
| occupied, the | Carbonic oxide | 133″ |
| Carbonic acid | 156″·5; | |
| but at low pressures, | Carbonic oxide | 11′ 34″ |
| Carbonic acid | 9′ 56″; |
I have lately had my attention again called to the subject, but have not yet been able to satisfy myself of the cause of this curious effect; nevertheless, as experiments do not always owe their value to the hypothesis which accompanies them, a few short observations on some made on this subject may be acceptable.
The effect is always produced by fine tubes at low pressures, but does not appear to belong to the mere obstruction by the tube to the passage of the gas, nor have I been able to produce it without a tube. A very fine needle-hole was made in a piece of platinum foil, and so arranged on a mercurial gasometer, that the pressure of a small column of mercury sent seven cubical inches of the following gases through in the times mentioned, namely—
| Hydrogen | 3′·8 nearly, taking a mean, |
| Olefiant gas | 9′·2; |
and when the pressure was increased, the same proportions in the times was observed. Other similar experiments gave similar results.
Slits, cut in platinum foil by the edge of a penknife, did not give so great a superiority to hydrogen as that mentioned above, and the proportion varied with different slits; still the hydrogen passed most rapidly, and a difference of pressure caused no difference in the relative times.
Three diaphragms were placed in different parts of the same tube, each being perforated with a small hole, but the effects produced in tubes were not observable here. Hydrogen passed in 3·8 minutes, and olefiant gas in 9·1 minutes.
