CHEMICAL SCIENCE. 229 



OX THE MECHANICAL PROPERTIES OF METALS. 



At the British Association, a report was presented by Mr. Fair- 

 bairn on the mechanical properties of metals, as derived from repeated 

 meltings, exhibiting the maximum point of strength and the causes of 

 deterioration. The experiments on which this report was founded 

 were undertaken at the request of the Association. Mr. Fairbairn 

 said that it was generally supposed that the strength of iron was dete- 

 riorated after three or four meltings, but the results of his experi- 

 ments proved that opinion to be erroneous. The metal experimented 

 on was Eglinton hot-blast iron, and the quantity was one ton. In 

 melting the iron the proportions of coke and flux were accurately 

 measured, and proper precautions were taken to prevent any differ- 

 ence in strength from variations in cooling and casting. The metal 

 was run into bars one inch square, lengths of seven feet were sup- 

 ported on two points, and weight was applied in the center till the 

 bars broke. It was found that the strength of the iron bars increased 

 up to the twelfth melting, after Avhich it diminished, and at each suc- 

 cessive melting deteriorated rapidly. The breaking weight at the 

 commencement was 403 Ibs., and the deflexion of the bar before 

 breaking was 1 ^ inch ; at the twelfth melting the breaking weight was 

 725 Ibs., and the deflexion If inch ; at the thirteenth melting the bar 

 broke with a weight of 671 Ibs. ; at the fifteenth, with 391 Ibs. ; at the 

 sixteenth, with 363 Ibs. ; at the seventeenth with 330 Ibs. At that 

 point the experiments were discontinued, as the quantity of iron had 

 been so far diminished by waste and by reserving specimen bars, that 

 no further trials would have been satisfactory. Mr. Fairbairn exhib- 

 ited specimens of the bars at the various meltings. The fracture of 

 the iron in the later experiment presented a marked change. In the 

 fifteenth melting there was a bright rim like silver surrounding the 

 interior, which was of the usual crystaline structure. This bright 

 silvery fracture extended in the sixteenth and seventeenth specimens 

 till it pervaded the mass, which then resembled cast steel. Mr. Fair- 

 bairn said he intended to have the different specimens analyzed, to 

 ascertain if the iron had undergone change in its chemical constitu- 

 ents as well as in the arrangement of its molecules. 



STRUCTURE OF IROX. 



The physical properties of iron differ considerably according to cir- 

 cumstances. Some species present also very striking differences in 

 their chemical composition. It is well known that no species of iron 

 is really pure. The most prominent of the substances commonly 

 found combined with iron is carbon, which is always present in a 

 greater or less quantity, and is nearly always accompanied by silica ; 

 which may possibly fulfil partially the same functions as carbon. Fuchs 

 directed his investigations more particularly to carbon ; this substance 

 is found in greatest quantity in pig-iron (particularly the sort called a 



