Prior to the century safes were not constructed to withstand the test of intense heat. Efforts were numerous, however, to render them safe against the entrance of thieves, but the ingenuity of the thieves advanced more rapidly than the ingenuity of safe-makers. And the race between these two classes of inventors still continues. For with the exercise of a vast amount of ingenuity in intricate locks, aided by all the advancement of science as to the nature of metals, their tough manufacture and their resistance to explosives, thieves still manage to break in and steal. The only sure protection against burglars at the close of the nineteenth century appears to consist of what it was at the close of any previous century—the preponderance of physical force and the best weapons. Among the latest inventions are electrical connections with the safe, whereby tampering therewith alarms one or more watchmen at a near station.

A classification of safes embraces, Fire-proof, Burglar-proof, Safe Bolt Works, Express and Deposit Safes and Boxes, Circular Doors, Pressure Mechanism, and Water and Air Protective Devices.

The attention of the earliest inventors of the century were directed toward making safes fire-proof. In England the first patent granted for a fire-proof safe was to Richard Scott in 1801. It had two casings, an inner and outer one, including the door, and the interspace was filled in with charcoal, or wood, and treated with a solution of alkaline salt.

This idea of interspacing filled in with non-combustible material has been generally followed ever since. The particular inventions in that line consist in the discovery and appliance of new lining materials, variations in the form of the interspacing, and new methods in the construction of the casings, and the selection of the best metals for such construction.

In 1834 William Marr of England patented a lining for a double metallic chest, filled with non-combustible materials such as mica, or talc clay, lime, and graphite. Asbestos commenced to be used about the same time.

The great fire in New York City in 1835, destroying hundreds of millions of dollars' worth of property of every description, gave a great impetus to the invention of fire-proof safes in America.

B. G. Wilder there patented in 1843 his celebrated safe, now extensively used throughout the world. It consisted of a double box of wrought-iron plates strengthened at the edges with bar iron, with a bar across the middle; and as a filling for the interspaces he used hydrated gypsum, hydraulic cement, plaster of paris, steatite, alum, and the dried residuum of soda water.

Herring was another American who invented celebrated safes, made with a boiler-iron exterior, a hardened steel inner safe, with the interior filled with a casting of franklinite around rods of soft steel. Thus the earth, air and water were ransacked for lining materials, in some cases more for the purpose of obtaining a patent than to accomplish any real advance in the art. Water itself was introduced as a lining, made to flow through the safes, sometimes from the city mains, and so retained that when the temperature in case of fire reached 212° F. it became steam; and an arrangement for introducing steam in place of water was contrived. Among other lining materials found suitable were soapstone, alumina, ammonia, copperas, starch, Epsom salts, and gypsum, paper, pulp, and alum, and a mixture of various other materials.

After safes were produced that would come out of fiery furnaces where they had been buried for days without even the smell of fire or smoke upon their contents, inventors commenced to direct their attention to burglar-proof safes.

Chubb, in 1835, patented a process of rendering wooden safes burglar proof by lining them with steel, or case-hardened iron plate. Newton in 1853 produced one made of an outer shell of cast iron, an interior network of wrought iron rods, and fluid iron poured between these, so that a compound mass was formed of different degrees of resistance to turn aside the burglar's tools. Chubb again, in 1857, and in subsequent years, and Chartwood, Glocker, and Thompson and Tann and others in England invented new forms to prevent the insertion of wedges and the drilling by tools. Hall and Marvin of the United States also invented safes for the same purpose. Hall had thick steel plates dovetailed together; and angle irons tenoned at the corners. Marvin's safe was globeshaped, to present no salient points for the action of tools, made of chrome steel, mounted in this shape on a platform, or enclosed in a fire-proof safe. Herring also invented a safe in which he hinged and grooved the doors with double casings, and which he hung with a lever-hinge, provided the doors with separate locks and packed all the joints with rubber to prevent the operation of the air pump—which had become a dangerous device of burglars with which to introduce explosives to blow open the doors.

Still later and more elaborate means have been used to frustrate the burglars. Electricity has been converted into an automatic warder to guard the castle and the safe and to give an alarm to convenient stations when the locks or doors are meddled with and the proper manipulation not used. Express safes for railroad cars have been made of parts telescoped or crowded together by hydraulic power, requiring heavy machinery for locking and unlocking, and this machinery is located in machine shops along the route and not accessible to burglars.

About 1815 inventors commenced to produce devices to show with certainty if a lock had been tampered with. The keyhole was closed by a revolving metallic curtain, and paper was secured over the keyhole. As a further means of detection photographs of some irregular object are made, one of which is placed over the keyhole and the other is retained. This prevents the substitution of one piece of paper for another piece without detection. A large number of patents have been taken out on glass coverings for locks which have to be broken before the lock can be turned. These are called seal locks.

Locks of various kinds, consisting at least of the two general features of a bolt and a key to move the bolt, have existed from very ancient days. The Egyptians, the Hebrews and the Chinese, and Oriental nations generally had locks and keys of ponderous size. Isaiah speaks of the key of the house of David; and Homer writes sonorously of the lock in the house of Penelope with its brazen key, the respondent wards, the flying bars and valves which,

"Loud as a bull makes hills and valley ring,
So roared the lock when it released the spring."

The castles, churches and convents of the middle ages had their often highly ornamental locks and their warders to guard and open them. Later, locks were invented with complex wards. These are carved pieces of metal in the lock which fit into clefts or grooves in the key and prevent the lock from being opened except by its own proper key.

As early as 1650 the Dutch had invented the Letter lock, the progenitor of the modern permutation lock, consisting of a lock the bolt of which is surrounded by several rings on which were cut the letters of the alphabet, which by a prearrangement on the part of the owner were made to spell a certain word or number of words before the lock could be opened. Carew, in verses written in 1621, refers to one of these locks as follows:—

"As doth a lock that goes with letters; for, till every one be known,
The lock's as fast as though you had found none."

The art had also advanced in the eighteenth century to the use of tumblers in locks, the lever or latch or plate which falls into a notch of the bolt and prevents it from being shot until it has been raised or released by the action of the key. Barron in England in 1778 obtained a patent for such a lock.

Joseph Bramah, who has before been referred to in connection with the hydraulic press he invented, also in 1784 invented and patented in England a lock which obtained a world-wide reputation and a century's extensive use. It was the first, or among the first of locks which troubled modern burglars' picks. Its leading features were a key with longitudinal slots, a barrel enclosing a spring, plates, called sliders, notched unequally and resting against the spring, a plate with a central perforation and slits leading therefrom to engage the notches of the slides simultaneously and allow the frame to be turned by the key so as to actuate the bolt. Chubb and Hobbs of England made important improvements in tumbler locks, which for a long time were regarded as unpickable.

Most important advances have been made during the century in Combination or Permutation Locks and Time Locks. For a long time permutation or combination locks consisted of modifications of one general principle, and that was the Dutch letter lock already referred to, or the wheel lock, composed of a series of disks with letters around their edges. The interior arrangement is such as to prevent the bolt being shot until a series of letters were in line, forming a combination known only to the operator. Time locks are constructed on the principle of clockwork, so that they cannot be opened even with the proper key until a regulated interval of time has elapsed.

Among the most celebrated combination and time locks of the century are those known as the Yale locks, chiefly the inventions of Louis Yale, Jr., of Philadelphia. The Yale double dial lock is a double combination bank or safe lock having two dials, each operating its own set of tumblers and bolts, so that two persons, each in possession of his own combination, must be present at a certain time in order to unlock it. If this double security is not desired, one person alone may be possessed of both combinations, or the combinations may be set as one. In their time locks a safe can be set so as to not only render it impossible to unlock except at a predetermined time each day, but the arrangement is such that on intervening Sundays the time mechanism will entirely prevent the operation of the lock or the opening of the door on that day.

Another feature of the lock is the thin, flat keys with bevel-edged notchings, or with longitudinal sinuous corrugations to fit a narrow slit of a cylinder lock. To make locks for use with the corrugated keys machines of as great ingenuity as the locks were devised. In such a lock the keyhole, which is a little very narrow slit, is formed sinuously to correspond to the sinuosities of the key. No other key will fit it, nor can it be picked by a tool, as the tool must be an exact duplicate of the key in order to enter and move in the keyhole.

Of late years numerous locks have been invented for the special uses to which they are to be applied. Thus, one type of lock is that for safety deposit vaults and boxes, in which a primary key in the keeping of a janitor operates alone the tumblers or guard mechanism to set the lock, while the box owner may use a secondary key to completely unlock the box or vault.

Master, or secondary key locks, are now in common use in hotels and apartment-houses, by which the key of the door held by a guest will unlock only his door, but the master key held by the manager or janitor will unlock all the doors. This saves the duplication and multiplicity of a vast number of extra keys.

The value of a simple, cheap, safe, effective lock in a place where its advantages are appreciated by all classes of people everywhere is illustrated in the application of the modern rotary registering lock to the single article of mail bags. Formerly it was not unusual that losses by theft of mail matter were due in part to the extraction of a portion of the mail matter by unlocking or removing the lock and then restoring it in place.

The United States, with its 76,000,000 of people, found it necessary to use in its mail service hundreds of thousands of mail pouches, having locks for securing packages of valuable matter. But these locks are of such character that it is impossible for anyone to break into the bag and conceal the evidence of his crime. The unfortunate thief is reduced to the necessity of stealing the whole pouch. Losses under this system have grown so small "as to be almost incapable of mathematical calculation."

Safe and convenient locks for so very many purposes are now so common, even to prevent the unauthorised use of an umbrella, or the unfriendly taking away of a bicycle or other vehicle, that notwithstanding the nineteenth century dynamite with which burglars still continue to blow open the best constructed safes and vaults, still a universal sense of greater security in such matters is beginning to manifest itself; and not only the loss of valuables by fire and theft is becoming the exception, but the temptation to steal is being gradually removed.