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ELECTRO-CHEMICAL POSITIONS OF WROUGHT IRON", ETC. 207 



Galvanometer Experiments. 



The bars of wrought iron and steels, &c, used in the experiments were 

 exactly T 2 <y 9 ^jths of an inch (7*5 millimetres) in diameter, and were cut as test 

 pieces from near the centre of bars of wrought iron and steel, manipulated as 

 near alike as possible for purposes of comparison. 



All the wrought iron and steel, &c, plates employed in 

 the following experiments, except where otherwise de- 

 scribed, were exactly three inches square (representing a 

 total surface area of exposure of eighteen square inches 

 for each plate, exclusive of the edges which were alike 

 in each case), and were of uniform thickness, and in shape 

 as shown in fig. No. 1. 



The bars and plates were of the chemical composition and Fig, l. 



possessed of the general physical properties, as shown in the preceding tables, 

 and with the exception of those covered with scale (magnetic oxide), were 

 all smoothly polished bright. 



The experiments on the various samples were conducted in each case in 

 precisely the same manner for purposes of exact comparison, and very many 

 times repeated, but in the same manner for corroboration, the results being 

 derived from exactly corresponding experiments in each case, the bars and 

 plates in the solutions being kept exactly the same distance apart, &c, in fact, 

 every precaution was adopted to insure accuracy. 



The records in the following tables of galvanometer experiments are the 

 result of some 3000 carefully made observations by the author, some of which 

 were thirty or forty times repeated to insure accuracy. 



It should be understood that the following experiments do not represent 

 fixed or permanent deflections ; but they are the results of a number of observa- 

 tions made in precisely the same manner in each case for purposes of exact 

 comparison between the various steels employed. 



In cases where necessary the author has recorded the highest and lowest 

 deflection noticed, in addition to the averages to illustrate the variations better. 

 In the galvanometer experiments the bars and plates were all immersed, one 

 pair at a time, in an equal measured quantity of sea- water, or other solutions, 

 and placed in galvanic connection at equal distances apart. The wrought iron, 

 &c, bar or plate, was connected with one terminal of a delicate galvanometer, 

 to the other terminal of which was attached the bar or plate of steel, &c. The 

 connections were made with insulated copper wires properly secured to the ends 

 of the bars or plates with screw clips. 



The measurement of the galvanic action is recorded in the tables. 



[Inserted April 5, 1883. — The galvanometer selected for these experiments 



