THE PERMANENCY OF WROUGHT-IRON STRUCTURES. 121 



expensive experiments conducted since the middle of 1884, at the Konig mine, 

 at Neunkirchen, near Saarbrucken, have completely solved the problem, have set 

 all doubts at rest. He says: " We can now distinguish dangerous from harmless 

 coal-dust. We know where we must forbid the use of fiery explosions altogether, 

 and substitute other means." 



The report of the experiments at the Konig minej we shall discuss in a later 

 issue. Professor Hasslacher, of Berlin, who acted as reporter of the Prussian 

 Commission, has made some general statements concerning them, from which it 

 appears that all kinds of coal-dust are capable of exploding violently when ignited 

 by such means as the electric spark, and that the extent of the explosion is much 

 greater with coal-dust than with fire-damp. These conclusions contradict those 

 of the earlier French Commission, which thus appears, on insufficient evidence, 

 to have underrated the danger from this source. The Prussian experiments go 

 to show that dust without the recognizable presence of fire-damp may become, 

 under some conditions, a destructive agent. A thorough study of the experi- 

 ments themselves will be required, in order to see how far they explain the most 

 impressive fact of all, namely, the fact that so many dusty coal-mines and coal- 

 breakers never have any explosions. No -theory which does not somehow ac- 

 count for this fact can be considered complete. 



Concerning the quantity of fire-damp generated in Prussian mines, Mr. 

 Althaus observes that 9,000,000 cubic meters escape annually from the shafts of 

 the very fiery Neu-Iserlohn I. mine; and that the seven most dangerous West- 

 phalian mines produce annually 39,000,000 cubic meters. He adds that all the 

 cities of Prussia could be lighted with the gas escaping from Prussian coal mines. 



The Pieler alcohol lamp and the Wolf benzine lamp are praised as the most 

 sensitive indicators of the pressure of fire-damp ; the former showing so small a 

 proportion in the mine atmosphere as 0.25 per cent, and the latter 2 per cent. 

 Since explosive mixtures contain more than 6 per cent, the warning thus given 

 would in most cases leave ample time for preventing the danger by increased sup- 

 ply of air, the only radical and effective safeguard. — Engineering and Mining Journal. 



THE PERMANENCY OF WROUGHT-IRON STRUCTURES. 



The following by Prof Rossiter W. Raymond, shows that the views 

 advanced in another article in the present number upon "The Fatigue of Met- 

 als," are not unanimously accepted by engineers and physicists : — \^Ed. Review.'] 



An elaborate report By Professor Thurston on the present condition of the 

 iron composing the structures of the New York elevated railroads, conclusively 

 shows that these structures have not been overstrained ; that they are made of 

 good material, and as good now as it was the day it was put in place ; that they 

 are well-proportioned and of a strength far beyond the danger limit for any one 

 of the possible causes of deterioration ; that they are not subject to risk of 

 crystalization or of any other source of injury to quality and strength known to 



