L. MECHANICS AND ENGINEERING. 489 



the gunpowder which promotes corrosion. In general, the 

 alloy composed of one third platinum and two thirds silver 

 is superior both to the pure platinum and to the German 

 silver; and this alloy has been admitted by the British As- 

 sociation Committee as the material for the reproduction of 

 standards of electrical resistance. An alloy of platinum and 

 iridium containing seven and one-tenth per cent, of the lat- 

 ter metal, proved as efficient in the protection of sensitive 

 fuses as the finest silver platinum, and has moreover the ad- 

 vantage of being much stronger, and more reliable as re- 

 gards uniformity of composition. It is, however, much less 

 fusible than the platinum silver, so that the latter has the 

 advantage when a large number of branch circuits of differ- 

 ent lengths are to be fired simultaneously. The larger the 

 percentage of iridium, the greater the resisting power of 

 the alloy. An equally efficient material is found in an alloy 

 of silver with twenty-five per cent, of palladium. The best 

 method of constructing a fuse, so as to insure a thoroughly 

 efficient priming, consists in preparing a very fine gun-cot- 

 ton powder, by taking dry pulp gun-cotton, or compressed 

 gun-cotton scraped off or broken up to powder, and sifting 

 this through muslin. The dust thus obtained is intimately 

 mixed, by means of a feather or hair-pencil, with sufficient 

 mealed gunpowder, or detonating powder, to make it flow 

 readily into a small cavity. When the breach of the fuse 

 has been fixed in position, this priming-paper may be poured 

 in, and made to surround it. 



ORGANIZATION OF THE UNITED STATES BOARD FOR TESTING 



IRON AND STEEL. 



The appointment of a government commission for the 

 purpose of experimentally determining the strength and 

 value of iron, steel, and similar materials for construction, 

 has been referred to upon another page, in a note stating 

 generally the objects which it was the problem of the com- 

 mission to realize, and its personnel. In pursuance of the 

 conditions of the act of appointment, the commission has 

 met and organized the following standing- committees to 

 take charge of special branches of their work, viz. : 



On Abrasion and Wear (A) : R. H. Thurston, C. E., chair- 

 man ; A. L. Holley, C. E., Chief Engineer D. Smith, U. S. 1ST. 



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