Another special type of steamship is the oil-tanker. Owing to the nature of her cargo a steamship that carries oil is far more liable to disaster through combustion than even a cotton-ship. Oil is carried not in barrels, but in bulk. At one time it used to be carried by sailing ships in barrels, but this meant that a great deal of trouble and space were unnecessarily expended. The first tank steamer was built in 1886 by Sir W. G. Armstrong, Mitchell and Company. Carrying a cargo of petroleum in bulk is obviously a fairly risky proceeding. Firstly, there is the terrible risk of fire, more especially as the ship must have engines and furnaces; but there is also the risk of the oil obtaining a good deal of impetus, unless guarded against, as the ship rolls. It can easily be understood that so considerable a weight moving about in liquid form--a shifting cargo, in fact, of a peculiar type--is likely to cause the gravest anxiety. The illustration facing page 246 will show to what trouble the designers and builders have been put in order to devise a safe oil-carrier. This represents the interior of a modern tank steamer built by Messrs. Sir W. G. Armstrong, Whitworth and Company, Limited, by whose courtesy this photograph of a model is here reproduced. First of all, it will be seen that the whole of the engines are placed aft, so as to be away from the dangerous oil. This characteristic, however, has recently been departed from, and in some ships the engines have been placed amidships, as in most steamships. Of this we might instance the s.s. _Phœbus_, built by Messrs. David J. Dunlop and Company, for the carrying of 9,000 tons of bulk oil. In such cases as these it is essential to insert a long, oil-tight tunnel which encloses the propeller shaft, but the drawback is that it takes up a good deal of valuable space from the ship’s hold. The accompanying illustration shows the holds divided up into a number of separate compartments by means of oil-tight bulkheads, which are further subdivided by a longitudinal bulkhead. But oil possesses the properties of expansion and varies according to the prevailing temperature. It is obvious, therefore, that room must be left for expansion. To meet this, then, a long trunk or slit is left to allow the oil to expand, so that after the ship has filled her holds to the proper height the cargo may yet be allowed to become larger in bulk. The model before us shows slits at the sides at the ’tween deck, so that this expansion may take place. It will be recognised where the ladders lead down to the holds beneath. These vessels carry powerful pumps, the oil being taken on board and discharged by this means. Oil is also employed as the ship’s fuel, and the boiler is kept as far away from the cargo as possible, but in order to counteract the possibility of the oil getting adrift and leaking into the after part of the ship, a separate small compartment is also added, so as more completely to divide the hold