MECHANICS AND USEFUL ARTS. 39 



The temperature of No. 1 had been above 600. The paper, cotton 

 batting, and box were charred ; the parchment and sealing-wax were 

 destroyed. 



The temperature of No. 2 had been as high as 580. The paper, 

 cotton, and box were charred. The parchment and sealing-wax were 

 destroyed. 



The temperature of No. 3 had been 350. Contents were much 

 less injured than those of No. 1 and No. 2, but were still greatly dis- 

 colored. The box was partially charred. 



The temperature of No. 4 was 287. The paper and cotton were 

 discolored. The box thoroughly dried and shrunken somewhat, but 

 not charred. The parchment was shrivelled and the sealing-wax 

 melted. 



The temperature of No. 5 had been 212. The parchment was 

 somewhat shrivelled, and sealing-wax melted ; but the paper, cotton 

 batting, and box were uninjured. 



In the safes filled with potash-alum, clay, and brick, with ammonia- 

 alum, salt and coke, and with sulphate of ammonia, salt, and coke, a 

 coarse porous wall around the interior wooden case was preserved after 

 the volatile matters had been driven out. In the cement safe, the cem- 

 ent retained about one-third of its water and the form perfectly. In 

 the gypsum and water safe, the plaster retained its form. It had parted 

 with about four-fifths of its water. (Strictly -||.) 



From the foregoing, it is evident that in keeping the temperature 

 down a given time, 7 Ibs. of sal-ammoniac are inferior to 14| Ibs. of 

 water from potash-alum; and these inferior to 15 f Ibs. of water and 

 sal-ammoniac, from ammonia-alum and salt; and these inferior to 13 

 Ibs. of water from the cement safe; and these inferior to 16 Ibs. of 

 water from the plaster and water safe. 



In the gypsum and water safe, 5 pounds of water were fixed in the 

 setting, and ]6 pounds were held by capillary attraction. These 16 

 were driven out at 212. There remained 5 in combination, at the 

 close of the experiment, to be driven out at the same temperature. In 

 the cement safe, G pounds were fixed in the setting, and 13f pounds 

 were held by capillary attraction. Of these 13f, 13 were driven out 

 at 212. There remained but f of a pound to be driven out at 212. 



In the alum safe, there were but 8 Ibs. expelled at 212. 



In summary the gypsum and water sate lost 16 Ibs. at 212 ; the 

 cement and water safe, 1 3 Ibs. ; the alum safe, 1 S Ibs. 



The water remaining to be expelled, at 212, from the gypsum and 

 water safe, was 5 Ibs. ; from the cement safe, was f lb. ; from the alum 

 safe, was 0. 



Not only was there no water to be driven out at 212, but 6| Ibs. 

 had been driven out at much higher temperatures, the last at 580. 



A cement safe, as ordinarily made, set and dried, of these dimensions, 

 contains a little more than half a pound of water to be driven out at 

 212. In a plaster safe, set and dried, there would have been but 5 

 Ibs. to be driven out at 212. In an ordinary alum safe, there would 

 have been less than 8 ; while in the gypsum and water safe, as 

 here prepared, there were 21 Ibs., which, by the process already de- 

 scribed, might have been increased to 50 Ibs. 



1 A part of this loss was evidently due to the moisture in the clay. 



