40 ANNUAL OF SCIENTIFIC DISCOVERT. 



The potash-alum safe lost altogether within l Ibs. as much water as 

 the plaster and water safe, but nearly one-half went out at temper- 

 atures from 212 to 58*0, a range destructive to books and papers. 

 The ammonia-alum and salt safe lost about 20 per cent, more of water 

 and sal-ammoniac than the cement safe of water alone, and yet did 

 not afford the same degree of protection, for the cement safe was heated 

 only to 28 7 , 1 while the ammonia safe was heated to 350. 



Experiment in a Furnace at a White Heat. Another experiment 

 was undertaken with four safes of the capacity of one cubic foot each. 

 Each contained a wooden box, enclosing a series of thermometers con- 

 structed to burst at given temperatures. 



No. 1 contained cement, 64 Ibs. ; water, 3| Ibs. This is cement 

 containing the quantity of water which remains after the filling is set 

 and dried. 



No. 2 contained plaster, 62| Ibs.; water, 12 Ibs. This is a plaster 

 of Paris safe, containing twenty-five per cent, more than the quantity 

 of water due to plaster set and dried. 



No. 3 contained alum, 33 Ibs.; pipe-clay, 33 Ibs.; brick, 19 Ibs. 

 This safe, with a smaller proportion of alum, is in extensive use in this 

 country. 



No. 4 contained plaster, 28 Ibs. ; gelatine, 2 1^ Ibs. ; water, 43 Ibs. 



These safes were placed in the same reverberatory furnace in which 

 the preceding experiment was conducted. There was this difference 

 between the experiments : The first was conducted with a constantly 

 falling temperature. This with a temperature carried from freezing 

 up to a white heat, and there maintained for thirty minutes ; and then 

 permitted to cool down. At the end of the first half hour, Nos. 1 and 

 2, which were least exposed, were red hot ; No. 3 was at low red, and 

 No. 4 was dark. 



At forty minutes, the condition was the same. At forty-two min- 

 utes, pronounced melting heat by the workmen, Nos. 1, 2 and 3 were 

 red, but 4 still dark equally. At fifty minutes, No. 4 became low red, 

 and No. 3 was burnt through and melted away at points nearest the 

 fire. At 60 minutes, No. 3 was at a white heat, and No. 4 was red. 



This white heat was maintained for thirty minutes, when the furnace 

 was opened and cooled down sufficiently to examine the condition of 

 the safes. 



No. 4 was burned so as to crack a little on one side, but was not 

 melted in any part. No. 3 was melted away from the top, front, and 

 two sides. The side farthest from the fire, and bottom, were alone 

 whole. No. 2 was scarcely less injured. The melting did not, how- 

 ever, extend so far down the sides. No. 1 , which was further from the 

 fire and sheltered by the other safes, was burned but not melted. 



The fire was again raised to the melting point, the furnace closed, 

 and the safes left in this heated chamber, slowly cooling down, from five 

 o'clock in the afternoon till ten o'clock the next morning. 



1 This elevated temperature, while there was still water in the cement, is mani- 

 festly due to the conducting' power of the soapstone upon which the wooden box 

 rested. 



2 I employ the term gelatine as expressing in a single word the substance ob- 

 tained by the action of boiling water from gelatinizable substances, like sea-weed, 

 of the variety known as Iceland moss, or potato starch, or animal membranes, 

 or from other similar vegetable aiid animal substances. 



