491
Chap. 3.] Effect of Conical Ajutages.
a vessel of quicksilver, was attached to B, and a scale to measure theascent of the mercurial column.
When the pressure of the steam in the boiler was equal to 30 poundson the inch exclusive of atmospheric pressure, and the steam cock Copened, (the hole in its plug was five-sixteenths of an inch in diameter)the mercury rose 9 inches in the vacuum tube B. When the steam wasat 40 pounds, the mercury rose 15J inches. At 50 pounds it reached over18 inches, at 60 pounds over 19 inches, and at 70 pounds 21 inches. At80 pounds it was only 21 inches, but on partially closing the cock it Sprungup to 22 inches. When the steam was at 90 pounds on the inch, the mer-cury feil to 20 inches, but on turning the plug of C it rose to 22 inches.These experiments were repeated several times and on different occasionswithout materially altering the results.
The effect of additional tubes inserted into the open end of A was nextobserved. Ten or twelve of these were made of tin plate, and of differentlengths and taper. The small ends of all were half an inch in diameter,and made very thin, so as to slide into A nearly up to the contracted part,and at the same time to present the least projection possible to the issuingcurrent. The effect of three of these tubes, two of which gave the bestresults, are stated in the following table. The tube No. 1 was 14 incheslong, and its wide end lj inches across. No. 2 was 27 inches long, and 1§in diameter at its mouth. No. 3 was five feet long, and its mouth or wideend 2J inches in diameter.
Pressure of steam in pounds Vacuum in inches of mercury vacuum with additional tubes.
on each square inch.
with apparatus No. 217.
No. 1.
No. 2.
No. 3.
30 -
9
-
- 10
11
—
40 -
- 15.5
-
- 17
18
10.5
50 -
- 18.1
-
- 20
20.5
—
60 -
- 19.6
-
- 20.5
22
—
70 -
- - 21
-
- 21.5
22.8
16.5
80 -
- 21
-
- 22
23.5
—
<<
- 22
-
- 22
23.5
—
90 -
- 20
-
- 20
21
—
- 22
-
- 22
—
—
In adjusting an additional tube it was moved tili its axis coincided withthat of A. This was ascertained by the mercury, which oscillated withevery movement of the tube, but always rose when it was in the positionindicated. On one occasion, when the mercury stood at 15 inches, theadditional tube No. 1 was slipped into A and the mercury feil to 12 inches;but this was caused by pushing the tube in too far, i. e. tili it touched thevacuum pipe—for on withdrawing it and swellmg out the end a little, themercury rose to 17 inches on the tube being re'inserted. A small additionwas made to the wide end of No. 1, so that it flared out like a trumpet:on trying it, the mercury stood two inches lower than before.
The fall of the mercury when the steam was raised to 90 pounds, wasquite unexpected. It was at first supposed to have been caused by awrong position of the additional tube, and then to some small object lodgedby the steam between the vacuum and the blowing pipes; but on exami-nation nothing of the kind was found. As the mercury still refused to rise,we tried another apparatus similar in all respects to No. 217, except beingof rather larger dimensions; but the same thing occurred. When thesteam was at 30 pounds the mercury stood at 7f inches—at 50 pounds 17inches—at 60 pounds 20 inches—at 70 pounds 22 inches—at 80 pounds23J inches—and at 90 pounds 20 inches ! Several experiments seemed