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PUBLIC RECORD OFFICE
Reference:
C.O.885
21 PUBLIC RECORD OFFICE, LONDON
ALLY WITHOUT PERMISSION OF THE BE REPRODUCED PHOTOGRAPHIC-
COPYRIGHT PHOTOGRAPH-NOT TO
4. Subsoil Drains.-A slanting sides is dug with and a shape as in diagram. enough to take the pipe, 10 inches in diameter.
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carefully graded trench with a fall of not less than 1 in 200, The bottom must just be wide which should be 6 inches to
The pipes are laid § inch apart, and covered with stones to ground level.
The stones will not get clogged if the ground around is covered with grass, and if that on the top side is not disturbed. If this should be done mud gets washed between the stones and pipes and the drain is spoilt, and must be re-laid. In connecting one subsoil drain with another nu extra slope should be given to the tributary just before it enters the other in order to provide an extra flush at the point of junction and prevent clogging.
125. Drainage, besides being useful in ordinary ways, is very useful on embankments or hill sides to intercept seepage water before it comes to the surface.
Larvicides:-
(a) Sea water.
() Kerosine at 7 c. a gallon.
e) Crude petroleum at 24 c. a gallon. (d) Larvicide, which costs 17 c. a gallon.
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(a) Sea rater-At Colon drains have been cut (as mentioned above), and sea water flows in. cannot enter freely it is not much use, as larvæ have been If the sea water found to grow in waters with an admixture of sea water below 40 per cent, of the latter.
(b) Kerosine.--This is not used alone, on account of its expense. In the process of burning, described below, it is used to dilute the crude oil.
126. (c) Larvicide is a mixture of carbolic acid, soda, and resin, prepared in the following way.
Contents:-
50 gallons crude carbolic of sp. gr. not greater than 0‘96. and containing not less than 15 per cent. phenol.
66 lbs. of resin (to be thoroughly powdered).
10 lbs, caustic soda, 98 per cent. pure, dissolved in
2 gallons of water.
The carbolic acid is put into a boiler with a steam coil in
the bottom, raised to the boiling point, and the resin gradually stirred in till thoroughly dissolved. soda solution is then added, keeping the mixture boiling, The caustic and stirred for five minutes.
The whole process takes 1 hours.
There is an engine used to provide the steam required which is kept solely for this purpose.
The cost of larvicide varies with the price of the carbolic, but is usually about 17 to 19 cents a gallon (about 9d.).
Larvicide is either mixed with the water containing the larvæ, and must then be used in such quantities as to make it a distinctly milky colour, or is used to mix with the crude oil.
127. Methods employed.—Cotton waste, dripping, spraying, burning and spraying.
128. Cotton waste method.—Cotton waste on the end of a stick is soaked in crude oil for 24 hours then placed so as to be partially in the water. This method is sometimes used on embankments and sides of hills where there is seepage, but requires attention at short intervals.
129. Drip Methods.-These are used in small streams or permanent drains. They require very little attention, in fact, may go on satisfactorily for weeks.
Barrels :-
A is an ordinary wooden barrel.
B is simply an ordinary tin wick holder inserted through
the side of the barrel near the bottom.