MECHANICS AND USEFUL AETS. 35 



THE CONSTRUCTION OF SAFES. 



The following is an abstract of a series of highly interesting and im- 

 portant researches recently made by Prof. E. N. Horsford, of Cam- 

 bridge, Mass., on the " Construction of Safes," intended for protection 

 against fire, dampness, rust, and frost: 



Protection against Fire. The experience of the last few years has 

 practically demonstrated, what might have been foreseen, that protec- 

 tion against fire can be relative only, not absolute. Fire-proof buildings, 

 so called, yield, when stored with combustible materials and for a long 

 time surrounded by flame. The best of fire-proof safes are destroyed, 

 when exposed to heat sufficiently intense and prolonged. This being 

 admitted, how shall the largest practical measure of protection against 

 fire be secured? First. By placing the books, papers, etc., to be pre- 

 served, in an incombustible enclosure, as of iron. Second. By sur- 

 rounding the books, etc., by a non-conductor of heat. Third, and 

 chiefly, by interposing between the incombustible enclosure, or outer 

 iron shell, and the wooden case containing the valuables, a substance 

 w r hich on the approach of fire, is converted into vapor, absorbing the 

 heat and carrying it. away. 



If the second and third be omitted, the contents of the safe will* be 

 destroyed as soon as the iron enclosure has become sufficiently hot to 

 set them on fire. If the third only has been omitted, the power of 

 preservation will be proportioned to the thickness of the layer of non- 

 conducting material ; and this, at the best, is relatively but for a' brief 

 period. If the second, only, has been omitted, since the protection 

 arising from vaporization is due to the absorption of heat in convert- 

 ing liquid or Solid substances into vapor, it will obviously be propor- 

 tioned to the quantity of substance so converted into vapor. A hun- 

 dred pounds of water will absorb twice as much heat in passing off in 

 the form of steam, as fifty pounds will ; and a safe that contains one 

 hundred pounds of water to be evaporated, will preserve its contents 

 in safety, through a fire in which a safe containing but fifty pounds 

 would be destroyed. A safe will then, manifestly, be a better protec- 

 tion against fire, in proportion as it unites within it, an incombustible 

 shell, the best non-conductor, with the largest amount of liquid or solid 

 to be converted into vapor, at a temperature not dangerous to the con- 

 tents of the safe. 



Dampness. Injuries from dampness in safes are not unfrequently 

 of a most serious character ; such as the mildew, and disintegration of pa- 

 pers, writings, &c. These injuries arise from the transmission of water 

 irom the fire-resisting composition, through cracks imperfectly closed 

 at the time of manufacture, or made subsequently by rusting; or 

 through the pores of the wooden case ; or by the freezing of the water of 

 the composition, by the expansion of which the walls are separated from 

 each other, and communication established between the filling and the 

 chamber of the safe. They may be prevented by so constructing 

 the safe as absolutely to prevent any communication of water or 

 vapor between the filling of the safe and the books and papers. 



In a climate like ours, a safe may be exposed occasionally to tem- 

 peratures below freezing. Any of the safes, as at present constructed, 

 cannot contain any considerable quantity of water above that in chem- 



