Safes. The manufacture of iron safes for the preservation of money and valuable papers has become one of great importance. The foundation of the plan on which fireproof safes are still constructed was laid by a Mr Richard Scott in 1801. Mr Thomas Milner in 1840 patented a fireproof safe embodying the same principle, but with some improvements. In 1843 letters-patent were granted to Messrs Tann for the use of a mixture of pounded alum and gypsum, previously heated and cooled, as a fire-resisting medium placed between two plates of iron, from 3 to 6 inches apart, which together form the wall of the safe. Milner's plan was to fill the jacket formed by the double-plated sides with sawdust, in which were packed a number of small tubes filled with an alkaline salt. These tubes burst when exposed to heat, and the sawdust becomes pervaded with moisture. When alum or sulphate of alumina is used there can be no charring till the large quantity of water these salts contain is expelled; and this is a slow process, as the heat causes a protecting crust of the anhydrons salt to form on the inside of the outer plate. Fireproof safes are still made on the same principle.
Safes are made to resist the efforts of burglars by making the outer wall of three plates, the centre one being of very hard and the other two of mild steel. All three are screwed together from the inside. By this arrangement the wall is made very difficult to drill. To prevent the door being wrenched off by wedges or other means, Messrs Chubb make the bolts of the lock, which emerge from the four edges of the rectangular door, to shoot diagonally, and so dovetail the door at the top, bottom, and sides to the frame of the safe (see LOCK).
Public safe-deposits for the safe-keeping of important documents, cash, gold and silver plate, and other valuables, have been constructed in recent years in many American cities, as well as in London and other large towns in Great Britain. Some of these contain a large number of safes, the building of the National Safe Deposit Company, Queen Victoria Street, London, having room for as many as 20,000. The brick walls of this company's great safe-vault are 3 feet thick, faced externally with firebrick and lined internally with cast-iron plates, 4½ inches thick, strengthened by imbedded wrought-iron bars. The separate compartments of the vault have doors, 12 inches thick, formed of metal plates of different degrees of hardness. These weigh 4 tons each, and are raised and lowered, portcullis-like, by hydraulic power. Chancery Lane Safe Deposit was opened in 1885. Its chief portion consists of four strong rooms 'armour-plated' and built on iron columns in vaults, but completely isolated from the external walls, so that armed patrols (armed watchmen guard the above safe-vault also) can, during the night, walk round, over, and under them. These rooms contain about 5000 separate safes and have doors weighing 2 tons each, which by a clockwork arrangement can only be opened at certain hours. The lock of a single safe cannot be opened unless both renter and custodian are present as each has a different key for the same safe. In the case of the Safe Deposit, opened in 1891, in St James Street, London, the walls, roof, and floor are formed of a triple thickness of Siemens-Martin steel together having a minimum thickness of 1½ inch. The middle plate is of hard and the two outer plates are of soft steel, and these three plates were riveted together by hydraulic pressure in such a way that the rivets swell out into the wider holes of the centre plate and therefore cannot be punched. As the rivets are made with a strand of hard steel, neither can they be drilled. See Protection from Fire and Thieves, by G. H. Chubb (1875). Various kinds of fireproof chambers are built with vaulted roofs and sides of strong masonry.