THE EFFECT OF PRESSURE. 



II 



sulphate used was prepared by dissolving almost the necessary amount of 

 pure crystals in a quantity of water, adding a small measured amount of 

 sulphuric acid, and making up to a liter. Then pieces of piano wire, care- 

 fully cleaned, were added. The acid acting on the iron thoroughly reduced 

 the solution, the amount of the acid having been so chosen that just the 

 necessary amount of iron dissolved to make the solution normal. Several 

 months were needed to remove the last traces of acid an essential condition. 

 The flask was connected with an automatic hydrogen generator whose cock 

 was always open, and when liquid was withdrawn through the siphon 

 hydrogen took its place. This also is represented in figure I. Thus after 

 having once prepared the solution, it could be kept indefinitely, perfectly 

 constant and always at hand. 



THE EFFECT OF PRESSURE. 



In the following work the term " porous iron " will be used for the sake 

 of brevity to designate the iron which had been reduced from oxide in the 

 manner described on pages 6 and 7. 



The results of a series of preliminary experiments with this porous iron 

 are given in table 1. 



The first two were made with samples which had merely suffered exposure 

 to air. The next four had received further treatment, having been put 

 into a small iron mortar such as is used in powdering rocks, and beaten with 

 a heavy hammer. Under this treatment the friable, porous iron became 

 compact and gained a shining metallic surface. The electromotive forces 

 of these samples were then measured after immersion in normal ferrous 

 sulphate. The cracked and powdered edges of numbers 2 and 3 were 

 covered with shellac, so that only the smooth metallic surface was exposed 

 to the solution. 



Table i. Preliminary experiments Electromotive force of iron against 



decinormal electrode. 



