38 ANNUAL OF SCIENTIFIC DISCOVERY. 



The results showed, that, as regards protection to be afforded by 

 vaporization from 212 to 220, the following substances ranked in 

 value in the order stated : Gypsum, gelatine, and water; Cement; 

 Glaubers salt and gypsum ; Sal soda and gypsum ; Alum. 



The question of using a composition which should give up vapor at a 

 temperature above 212 only, was tested in the use of a mixture of 

 sulphate of ammonia and common salt, diluted with powdered coke, 

 which, on the application of heat, yielded sal ammoniac. Experiments 

 were also made with a mixture of ammonia-alum and common salt, dilu- 

 ted, like the above, with coke. This yielded water in addition to sal 

 ammoniac. Clay and powdered brick were substituted for coke. They 

 gave results inferior to all except the potash-alum. 



In addition to these laboratory experiments, a series were undertaken 

 on a scale of such magnitude as to render the results of more direct 

 practical value. As the object was to determine the relative excellence 

 of different kinds of safes in which all the circumstances of exposure 

 were the same, it was conducted with great attention to details, and 

 was, on many accounts, the most important ever made of which any 

 record, has been preserved. 



Experiments in Reverberalory Furnaces. Five wrought-iron safes were 

 constructed, each of one cubic foot capacity. For each, a small wooden 

 box four inches in the clear, and three-quarters of an inch in thickness, 

 was prepared to represent the inside case. When in place, there was 

 a space for composition of three inches thickness on every side of the 

 box. In each wooden box was placed a piece of parchment, some 

 white writing paper, cotton batting, a piece of sealing-wax, a self- 

 registering thermometer ranging to 600, and a series of small ther- 

 mometers bursting at given temperatures. 



No. 1 contained sulphate of ammonia, 15.5 Ibs. ; common salt, 15.5 

 Ibs. ; powdered coke, 24 Ibs.; wooden box, 2 Ibs.; iron shell, 27 Ibs. 

 Total, 84 Ibs. 



No. 2 contained potash-alum, 26 Ibs. ; pipe-clay, 26 Ibs. ; brick, 28 f 

 Ibs. ; dry cement, to fill, f Ibs. ; wooden box, 2 Ibs. ; iron shell, 28 f Ibs. 

 Total, 11 2^ Ibs. 



No. 3 contained ammonia-alum, 26 Ibs. ; common salt, 13^ Ibs. ; 

 coke, 16 Ibs. ; wooden box 2^ Ibs. ; iron shell, 29^ Ibs. Total, 87^ Ibs. 

 No. 4 contained cement, 60 Ibs. ; water, 19|- Ibs. ; soapstone front, 9 

 Ibs. ; wooden box, 2 Ibs. ; iron shell, 30 Ibs. Total, 120| Ibs. 



No. 5 contained plaster of Paris, 50 Ibs.; water, 21 Ibs. ; dry cement, 

 to fill, 9 Ibs. ; wooden box, 2 Ibs. ; iron shell, 28 Ibs. Total, 110 Ibs. 



These safes were carefully introduced into a reverberatory furnace 

 from which a discharge of twenty thousand pounds of molten iron had 

 just taken place, and when the walls were nearly at the temperature 

 of melted iron. The safes were placed on the bottom of the furnace, 

 the door closed, and after adjusting the draft so as to permit the fur- 

 nace to cool slowly down in the usual way, the safes were left from five 

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



On taking the safes from the furnace, they were first weighed. No. 

 1 had lost 8j Ibs. ; No. 2, 1 15| ; No. 3, 2 16 ; No. 4, 13 ; No. 5, 16. 



l This is the common alum safe, except that one-third of alum was employed 

 instead of one-quarter. 



-' One pound of this, and of each of the preceding two, is due to the charring of 

 the wooden box. 



