11,75.] bUO [Oresson. 



Under these conditions if there was any effect to be had from the in- 

 fluence of the magnetic force, the bar should incline to break either at 

 the central pole or at the neutral point between the poles. 



The resuUs of the experiments showed that there was no inclination to 

 a choice of either location as the place of fracture. 



The conclusion arrived at, is, that the condition o^ magnetic polarity 

 does not in any way influence the strength of steel bars. With refer- 

 ence to the soft iron bars the comparison was not made, for the reison 

 that they would not remain magnetic unless surrounded by the galvanic 

 coil, in which case they became heated by the action of the current. 



How far a change from fibrous to crystalline structure is effected by the 

 influence of magnetism has not baen ascertained, or whether there is any 

 deterioration of the strength of iron or steel on such account. 



Iron telegraph wires, in the course of time become brittle, and to such 

 an extent that if the usual method of uniting them by winding each upon 

 the other is attempted, they are frequently broken in the process. 



From this it would appear that the passage of a strong galvanic cur- 

 rent produces some molecular change affecting the strength of iron. 

 Sach conducting wires, however, are not necessarily or even usually mag- 

 netic. There can be no doubt, however, as to the deteriorating effect of 

 galvanic force as an accelei-ator of oxidation or the solution of a metal. 



Observations upon Iron Bridges and structures subjected to atmos- 

 pheric influences and upon Boilers exposed to the action of heat and the 

 chemical agents contained in ordinary waters lead to the conclusion that 

 galvanic force is usually as great, and frequently a far greater cause of 

 deterioration than mechanical wear. Indeeed all of the operations of 

 nature, oi'ganic and inorganic, both constructive and disjunctive, involve 

 the production of more or less galvanic force or are the results of its 

 action. 



Motion, unaccompanied by any other apparent change than that of 

 place, is a disturber of electric or galvanic equilibrium, and the converse 

 is equally true. If it were possible to produce perfectly pure and homo- 

 geneous iron, then the generation of destructive galvanic currents by the 

 contact of sheets or bars would not take place. 



By exercising care in the selection of iron, especially that used for 

 steam boilers, the deterioration from galvanic action can be reduced to a 

 minimum. 



Many steam boilers have come under my observation in which the cor- 

 rosion was but slight, and affected all parts equally, others in which the 

 metal of a single sheet only was attacked, the corrosion of which sheet 

 protected the remainder of the boiler almost as ef6.ciently as if the sheet 

 had been replaced by one of the metal zinc . 



The most striking instance of the effect of introducing a sheet of metal 

 of greatly differing electro-condition, that occurs to me, is that of a 

 boiler which had been in use for a considerable length of time without 

 showing any unusual tendency to corrosion, when from some cause it be- 

 came necessary to replace a sheet by a new one. 



