The exterior case is made of well-seasoned elm 1½ in. thick, iron bound, and screwed together with water-tight packing between the joints, also cemented with pitch. The interior case is made of stout sheet copper; the case has two loading holes corresponding in size to two holes in the deck, or top of the exterior case. These holes are made sufficiently large to load with gun-cotton discs, if preferred. The loading holes are fitted with corks, which are inserted before screwing on the brass cap, to prevent any chance of accident through friction in screwing on the cap; the bushing has the thread of the screw on the outside for the same reason. If thought necessary, the cork can be cemented over before screwing on the cap, which will render the joint doubly secure from leakage. The centre of the copper case has a stout copper tube, which is soldered to the top and bottom surfaces of the copper case, the charge being all round it; into this centre tube is screwed the priming case. It should be understood that both the exterior and inner cases are thoroughly water-tight, so that in the event of the outer case being damaged, still the charge in the interior case is preserved perfectly dry, the cases being altogether independent of each other. The capacity of the copper case of the large torpedo is such that it will contain 77 lbs. of water; the capacity of the small one, 28 lbs.; from these can be determined the quantity of any explosive agent with which it may be desired to charge either torpedo. The charges of various powders the torpedoes will contain are as follows:— Large Torpedo. Small Torpedo. lbs. lbs. Glyoxilin 47 16 Schultze’s blasting powder 60 22 Compressed gun-cotton 60 22 Picric powders 73 26 Rifle grained powder 76 27 Horsley’s original 80 28 Horsley’s blasting powder 85 30 Nobel’s dynamite 100 35 The above must be considered an approximation, since much will depend upon the labour expended in packing the torpedo. Some of the powders named have not yet been manufactured on a large scale. The priming case is made of stout sheet copper, and contains a large bursting charge, which may be either rifle grained powder or a stronger explosive, which is recommended. [Illustration: (D) SECTION.] [Illustration: (E)]