TEANSACTIONS OF SECTION B. 303 



especially to such specimens as have been found to possess anomalous characters. 

 Of these characters the evolution of ammonia from freshly fractured surfaces is 

 among the most striking. 



3. Colour Tests for the Estimation of Sulphur and Phosphorus in Iron or 

 S h eel. By A. Vernon Harcourt, M.A., F.B.8., Lee's Reader in 

 Chemistry at Christ Church, Oxford. 



A weighed portion of finely divided iron or steel is treated in a flask with diluted 

 sulphuric acid (previously boiled to expel air), with the addition of a lump of pure 

 zinc. The sulphur contained in the iron is evolved as sulphuretted hydrogen,' 

 which, passing into a foot-glass containing lead solution, colours the latter. The 

 phosphorus is evolved as phosphoretted hydrogen, which passes through the lead 

 solution into a second foot-glass containing a dilute solution of silver nitrate. The 

 flask is heated gradually to boiling, and then the depth of colour in the two foot- 

 glasses is compared with two sets of standards. 



4. Some Experiments with the Voltaic Induction Balance. 

 By W. Chandler Roberts, F.B.S., Chemist of the Mint. 



The author stated that this instrument, which we owe to Professor Hughes, 

 the discoverer of the microphone, appeared to be one of no ordinary importance ; 

 and although the experiments about to be described were far from complete, they 

 possessed sufficient interest to warrant their being submitted to the Section. He 

 then described and exhibited Professor Hughes' instrument, showing the extreme 

 delicacy by which changes in the indueed current were indicated by the micro- 

 phone and telephone. 



The relative values of different metals, as indicated by the induction balance, 

 do not accord with the values usually accepted as representing the relative con- 

 ductivities of the respective metals ; and this being the case, Mr. Roberts had 

 ascertained what relation the indications given by alloys when under the influence 

 of the induced current bear to their electric conductivities. 



The experiments on a comprehensive aeries of alloys proved that, in the case of 

 alloys of certain metals, the induced current curves closely resembled those repre- 

 senting electric conductivity ; but that in certain other cases the induced current 

 revealed differences that had hitherto escaped observation. As an example, Mr. 

 Roberts alluded to the curve of the copper-tin alloys, in which there is a sudden 

 break between the points, representing two alloys, which only vary by a single 

 equivalent, or by 6-4 per cent, of copper. These two alloys are widely different in 

 colour, fracture, density, and structure, and the induction balance at once afforded 

 evidence of a marked difference not shown in Matthiessen's curve of electric 

 conductivity. 



It is known that certain metals when alloyed undergo a molecular change, and 

 that an allotropic condition may in some cases be induced by alloying a metal with 

 a small quantity of another, facts which will doubtless receive careful examination 

 from those who are pointing to the non-elementary character of certain metals. 



Mr. Roberts then referred to the question of applying the induction balance to 

 the assay of metals. In the case of gold-silver alloys the instrument will show 

 the presence of less than 2 grains of gold in the pound of silver. On the other 

 hand, the silver-copper alloys used for coinage are situated at the flat portion of the 

 curve, so that it is impossible to detect even considerable differences in their com- 

 position, and these alloys, which are very peculiar to their nature, appear to be 

 greatly affected by annealing. More hopeful results were obtained with the gold- 

 copper alloys, and Mr. Roberts demonstrated a difference of 1 per cent, in the 

 standard of two gold discs, which, though far short of the existing method of 

 assay in delicacy, appeared to afford grounds for the belief that very accurate 

 results will ultimately be obtained. 



