208 ANNUAL OF SCIENTIFIC DISCOVERY. 



the process of pressing and annealing, consume at least twice as much time and 

 labor as are employed in working slag. "From those simple, yet clear data.," 

 observed Dr. Smith, "we can fairly infer that the cost of making clay bricks 

 will be double that of making blocks, tiles, or more decorative and valuable 

 articles from slag. By extending this calculation to other products, such as 

 marble slabs, columns, carved architectural ornaments of stone, etc., and in 

 our estimate contrasting the plastic power of fusion available in slag with the 

 laborious hewing and fashioning by mechanical means required for blocks of 

 marble and other stones, we may arrive at still more satisfactory results in 

 proving the commercial value of slag." 



The samples which were exhibited and examined by the auditory excited 

 general admiration, from the closeness of the texture, the height of the polish 

 and the beauty and apparent durability of the articles. Some of them had 

 been made from the slags of American furnaces, others from those of the fur- 

 naces of France and England ; and it was evident, from their inspection, that 

 the commercial value expressed in the above calculation was by no means 

 extravagant. London Mining Journal. 



FUSIBLE SAFETY-PLUGS. 



It is well known that plugs of metal composed of some alloy fusible at a 

 comparatively low temperature, have been prescribed for steam-boilers, especially 

 those of the steamboats on our "Western waters, so as to insure greater safety 

 to the traveling community, as well as to engineers themselves. Some have 

 contended that these plugs were a perfect protection against too high steam 

 pressure (whereby its heat is increased) and also against low water in boilers ; 

 others again have contended that they were of no use whatever, not being 

 uniformly reliable, either as to the degree of heat at which they will melt when 

 new, also by altering their nature entirely when used for some time, so as to 

 be in no manner different from the metal of the boiler itself as it respects melt- 

 ing. This subject being referred by the St. Louis Association of Steamboat 

 Engineers to a committee of its members, they have examined into the matter 

 and made a report of their labors. In that report they mention the experi- 

 ments with Easton's and Evans's safety-guards of fusible alloys, and point out 

 their uncertainty, and conclude as follows: 



" Finally, after having given this subject our most careful consideration, and 

 after having proven our opinions, by many years' experience as practical en- 

 gineers, during which we have had the most ample means of determining the 

 value of alloy safety-valves, we have arrived at the candid conviction that they 

 are useless to the engineer, and of no protection to the traveling public. If Con- 

 gress shall still insist upon the use of fusible alloy safety-guard, we respectfully 

 ask that it will cause such investigation to be made and such manufactures of 

 these alloys established as will insure them to be uniform in operation and 

 satisfactory in their results (if these are practicable), and that the mechanical 

 device, by which the alloy may be applied, be left open to the inventive ge- 

 nius of the country; the best of which to be determined from time to time 

 by some proper and competent authority." Scientific American. 



