254 Professor John Oliver Arnold [Feb. 23, 



Brass often consisted of two constituents, namely a ground mass 

 of true brass of formula Cu2Zn and a eutectic corresponding to the 

 formula ZuoCu. Upon a mass so constituted a feeble saline electro- 

 lyte attacked in the first instance the constituent rich in zinc, whilst 

 the constituent rich in copper assumed an electronegative position, 

 acting, of course, as the cathode of the couple. 



But, when the eutectic had been transformed into spongy copper, 

 the latter assumed the electro-negative position and the true brass 

 became the anode, hence gradually transforming the whole mass from 

 Muntz metal into spongy copper. In the case of the " Prodano," the 

 electrolyte was proved beyond all doubt to have consisted of fatty 

 acids due to the use of improper lubricants. Little by little the 

 brazed seam was cuprified until the junction became so weakened 

 that at a pressure of only 130 lb. per square inch, the port main 

 steam pipe opened for a space of 6 feet and consigned four men to an 

 agonising death. 



This research, made at the Sheffield College under instructions 

 from the Committee of Lloyd's Register, had resulted practically in 

 the abolition of brazed copper main steam-pipes, and the substitution 

 therefor of rolled steel. 



Reaching the third section of the lecture, this undoubtedly must 

 be regarded in the steel age as the most important, since it dealt with 

 steel. Taking the base of steel, namely pure iron, this had a similar 

 structure to that of pure gold, but the etching figures exhibiting the 

 molecular orientation in the allotrimorphic crystals of this metal were 

 seldom revealed by ordinary etching. 



Broadly speaking, iron was converted into steel by the addition 

 of the element carbon, and researches made in the Sheffield College 

 had indicated that steels naturally divided themselves into three 

 classes, namely, unsaturated, saturated, and supersaturated steels. If 

 • 3 per cent, of carbon were added to steel, the carbon converted 

 one-third of the iron into the constituent pearlite, and in such a 

 steel, as cast, the iron or ferrite frequently arranged itself into a 

 pattern, indicative of cubic crystallisation exactly comparable with the 

 figures observed by Wiedmanstaten in the non-terrestrial steels called 

 meteorites. In saturated steels, just sufficient carbon approximately 

 0-9 per cent, had been added to the ferrite to convert it totally into 

 the constituent pearlite, a definite mixture corresponding to the 

 formula (2lFe -f FegC). This definite mixture presented at least 

 three well-marked phases having different mechanical properties deter- 

 mined by the state of the division of the carbide FegC. These phases 

 might be differentiated by distinguishing the involved carbide as 

 emulsified, normal and laminated, the latter being the pearly con- 

 stituent of Sorby, presenting a play of gorgeous colours, determined 

 by the varying thickness of the laminae acting like mother-of-pearl 

 in nature, or the interference grating in science. Through no scien- 

 tific foresight, but as a matter of fact by an act of carelessness, there 

 had been secured at the Sheffield College a section showing the trans- 



