416	NICEOLLS'S  SEAMANSHIP AND  NAUTICAL KNOWLEDGE
The conveyance of food is a specialised trade arid detailed instructions
-are issued to their officers by the firms engaged in it regarding such
cargoes, as apples, oranges, bananas, cheese, eggs, butter, beef and other
com modi ties v^hich are "chilled" as distinguished from meat which is
kept frozen. The stowage of the goods, their supervision during
transit and their handling when being loaded and discharged, are
described in the private book of instructions issued by the company,
and particular reference is made to the pre-cooling temperatures of
the chambers at shipment, the maintenance temperatures during the
passage and the temperatures desirable on opening up the chambers
prior to discharging. For example, the temperature during the voyage
for frozen meat is 15°; for chilled meat about 29°; for apples and butter
about 33°; oranges and cheese about 40°; bananas about 53°.
A Tanker is a ship specially designed to carry liquid cargoes such as
oils, molasses, and creosote in bulk, about 7,000,000 tons of various
oils being imported annually into the United Kingdom. Such vessels
are divided into separate oil-tight compartments by means of transverse
and longitudinal bulkheads.'
The compartments of an oil-carrying ship are indicated in the
illustration (see p. 417) and, beginning at the bow, we note—
 1.	The forepeak tank forward of the collision bulkhead.
 2.	A hold for dry cargo with two deep water ballast tanks for
trimming the ship.
3.	A cofferdam extending the whole breadth of the ship and the
depth of the tank. Cofferdams must be fitted at each end
of the oil tanks to protect the other parts of the ship from
gas. The space between the bulkheads of the cofferdam
must be at least 3 feet.
*. j± series of tanks numbered 1 to 11. The diagonal lines across
each compartment denote that a longitudinal bulkhead is
fitted. The side summer tanks are shown both in the profile
and in the plan.
5.	This ship has two oil pump rooms, one midway along and the
other at the after end of the tanks. The pump room in the
forward cargo hold is for the water ballast tanks.
6.	Abaft the after pump room is the cofferdam separating the
oil tanks from the engine and boiler spaces. Note the
balanced rudder and the cruiser stern of this ship.
7.	The plan shows 'the position of the hatches giving access to the
expansion trunks and to. the summer tanks.