36 ANNUAL OF SCIENTIFIC DISCOVERY. 



ical combination, without the danger of bursting by cold. This open- 

 ing of the seams of the safe at once exposes the contents of the case 

 to the exhalation of moisture from the filling. The protection against 

 this kind of injury manifestly lies in such construction of the safe as 

 will provide for the expansion consequent on freezing, without opening 

 the joints or seams of the various parts. 



Rust. This is one of the agencies by which communication be- 

 tween the filling and the chamber of the safe is effected after the lapse 

 of time ; and by which the contents of the chamber become damp. 

 It may be prevented by consuming the oxygen of the air which would 

 otherwise act on the iron. Chemical compositions are prepared which 

 will, by absorbing the oxygen, perfectly protect the iron from corrosion 

 or rust, even in the presence of air and water. 



Varieties of Safes in use. The safes at present in use differ from 

 each other in various respects, but chiefly in the capacity of the com- 

 position employed, to yield vapor. 



The earliest safes were designed chiefly to protect treasure against 

 burglary, and were distinguished for their strength. Next came safes 

 having non-conducting walls as protection against fire. In 1840, a 

 safe appeared which took advantage of the principle of vaporization of 

 water as protection against fire. The alum safe, upon the same prin- 

 ciple was devised in 1843. The gypsum safe, also on the same princi- 

 ple, has long been in use. The cement safe, in which hydraulic cem- 

 ent is substituted for gypsum, has been many years in use. In the 

 English safe of Milner, invented in 1840, the space between the 

 iron shell and wooden case is occupied with closed tubes containing 

 water, these tubes being imbedded in saw dust. On exposure to fire, 

 the tubes burst, and the water, flowing into the sawdust, is converted 

 into vapor, and escapes through the joints of the iron shell. 



In the alum safe, invented by Messrs. Tann, of England, and a 

 modification of which is produced in this country, the vapor is derived 

 from the water of crystallization of the alum. Twenty per cent, of the 

 weight of the alum is converted into vapor at 212, and eighteen more 

 at 250. The remainder is given up only at a heat destructive to the 

 contents of the safe. 



In the ordinary gypsum safes, the surplus water added in the mixing, 

 if it does not remain to do injury by charging the case and books with 

 dampness, or by freezing, is in process of time exhaled until there re- 

 mains only what has entered into chemical combination. This latter 

 amounts to twenty per cent. Of this, ten per cent, is given up at 212, 

 and half of the remainder below 300. The cement safes, as they are 

 usually prepared, contain, after setting, and after time for giving up 

 the surplus water, about six per cent, of water. Of this, one per cent. 

 goes out at 212. As the Alum safes are prepared in this country, the 

 alum is mixed with pipe clay, and this mixture with fragments of brick, 

 the former to absorb the water as the alum melts and to facilitate the 

 vaporization ; the latter to give support and prevent the composition 

 from falling when the alum melts. The proportion of alum is about 

 one quarter of the whole. This would give of water from the compo- 

 sition, at 212, only five per cent, and at 250, four and a half per 

 cent, more, or only nine and a half in all. If the alum were raised to 

 the proportion of one half of the whole mixture, it would give up but 



