-
THE HONGKONG GOVERNMENT GAZETTE, 27TH SEPTEMBER, 1890.
969
The sewage will flow so rapidly through the sewer that each gallon of sewage will be in the sea within a few minutes of its leaving the house, say in twenty minutes as an extreme limit. Supposing that the people of Hongkong are so neglectful of their house-drains, that all the sewage enters the public sewer in a state of active putrefaction; then each gallon will evolve, in transitu, about 0'4 cubic inch of gas, or in all 700 cubic feet of gas per day, or sufficient to fill a 12"-pipe, for a length of about 90 feet.
It is to be hoped that the house-drains will not be neglected, but even if it were, the amount of real yas to be evolved from the sewerage in the public sewers would be trivial.
Appendix II.
Movement of Air in Sewers.
SANTO CRIMP on the movement of sewer-air at Wimbledon.
Proceedings Ins. C.E. Vol. XCVII. Part III. Page 383 et seq.:—
SEWER-AIR EXPERIMENTS AT WIMBLEDON.
Month.
Temperature of
Air.
Temperature of Sewer-Air.
Difference.
Temperature of
Sewage.
No. of Days.
Up.
Down.
Both.
January,
35.73
42.70
+6.75
46.30
13
February,
34.75
42.30
+7.55
44.75
19
29
March,..........
38.50
42.10
+3.60
45.41
13
27
1
April,..
43.50
44.50
+1.00
47.60
19
30
i
May,
52.00
49.20
-2.80
50.10
11
26
June,
57.70
54.25
-3.45
53.90
3
27
July,
58.00
56.65
-1.35
54.80
2
28
August,
59.10
57.75
- 1.35
55.65
27
September,
55.80
57.70
+1.90
56.70
5
20
October,
44.70
53.10
+8.40
51.25
November,.
46.40
50.65
+4.25
48.30
26
December,
41.00
48.85
+7.85
40.60
2 2 2 2 2 2 N 2 2 2 os
12
8
19
11
19
11
3
2
12
5.
1
5
9
Mean. 47.26
Mean. 49.98
Mean. 49.61
Total. Total.
97
273
Total. 88
}
The sewer experimented upon was 1,860 feet long; and had an average gradient of about 1 in 19, so that it was nearly as steep as the sewers of Hongkong.
66
“During the entire series of experiments the actual volume of air recorded as passing down hill exceeded that recorded " 'as passing up-hill by nearly one-third, Whilst down-hill currents were recorded as on 273 days as against up-hill currents
*
on
97 days. ****
15
The direction of the current was determined by that of the wind; whilst the currents were "either strong or weak or imperceptible, according as the wind was fresh or light, or calms prevailed.
** In "
£6
แ
*
*
'gusty weather the currents were at one moment rapidly up-hill, and then suddenly the direction would be reversed, this" "occurring again and again in the space of a few minutes."
*
*
*
*
*
In a large brick sewer the currents were found to be in opposite directions, at one and the same time, at two points' not more than 200 yards distant from each other."
These exhaustive experiments shew clearly that there is no permanent upward current. They agree exactly with what was found to take place in the Peak Drainage.