TRANSACTIONS OF SECTION A. 773 



results, which were obtained in the early part of the investigation, when linen 

 soaked in strong brine was rubbed on aluminium, was ultimately traced to one 

 layer of moist linen of the thickness of a pocket-handkerchief, allowing the finger 

 to act through it, so that an odour was sometimes noticed on rubbing aluminium 

 with the piece of linen soaked in brine. For it was found that when two or more 

 layers of the same linen soaked in the same brine were employed to separate the 

 finger from the aluminium during the rubbing no smell could be detected. 



From the preceding it seems that the smell in these cases is evolved partly by 

 contact with the finger, partly by the action of the solution of salt, and partly by 

 the rubbing of the solid particles of salt against the metals. That the friction of 

 solid particles against metals is operative in evolving smells is also illustrated by 

 the smell noticed M'hen iron is filed, or when aluminium, iron, or steel is cleaned 

 with glass-paper or emery-paper in the air. Indeed, the smell thus evolved by 

 aluminium Mrs. Ayrton finds particularly offensive. A slight smell is also noticed 

 if iron or steel be rubbed in the air with even a clean piece of dry linen, and each 

 specimen of the copper group, with the exception of the phosphor-bronze, which 

 was tried in this way, gave rise to a faint, rather agreeable smell. No indication 

 of odour could, however, be thus produced with aluminium or zinc when both the 

 metals and the linen rubber were quite clean. It should, however, be borne in 

 mind that all these experiments, where very slight smells are noticed, and espe- 

 cially when the odour rapidly disappears on the cessation of the operation tliat 

 produced it, are attended with a certain amount of doubt, for the linen rubber 

 cannot be freed from the characteristic smell of ' clean linen,' no matter how care- 

 fully it may be washed. 



Before, tlien, a metal can evolve a smell, chemical action must apparently take 

 place, for rubbing the metal probably frees metallic particles, and facilitates the 

 chemical action to which I shall refer. All cliemical actions, however, in which 

 metals take part do not produce smell ; for example, no smell but that of soda, or 

 of sugar, respectively, can be detected on rubbing any single one of the series of 

 metals that 1 have enumerated with a lump of wet soda, or a lump of wet 

 sugar, although chemical action certainly takes place. Again, no metallic smell 

 is observable when dilute nitric acid is rubbed on copper, German-silver, phosphor- 

 bronze, tin, or zinc, although the chemical action is very marked in the case of 

 some of these metals. Weak vinegar or a weak solution of ammonia is also 

 equally inoperative. On the other hand, merely breathing on brass, copper, iron, 

 steel, or zinc, which has been rendered practically odourless by cleaning, produces 

 a very distinct smell, while a very thin film of water placed on iron or steel 

 evolves a still stronger odour. Such a film, however, produces but little eflect 

 with any of the metals except these two ; and if the wliole series is lightly touched 

 in succession with the tongue, the iron and steel smell as strongly as when 

 breathed on, the German- silver more strongly than when breathed on or covered 

 with a water film, and the other metals hardly at all. 



Now, as regards the explanation of these metallic smells, which have hitherto 

 been attributed to the metals themselves. This, I think, may be foimd in the 

 odours produced when the metals are rubbed with linen soaked in dilute sulphuric 

 acid. For here, apart from any contact of the metal with the skin, the aluminium, 

 tin, and zinc are found to smell aUke ; the copper group also smell alike, and the 

 iron and steel give rise to the characteristic ' iron ' smell, which, iu this case, can 

 be detected some feet away. Now, it is known that when hydrogen is evolved 

 by the action of sulphuric acid on iron, the gas has a very unpleasant smell, 

 and this. Dr. Tildeu tells me, is due principally to the presence of hydro- 

 carbons.' I have been therefore led to think that the smell of iron or steel when 



' I am informed that as all ordinary iron and steel contain, beside carbon, the 

 elements phosphorus, sulphur, and silicon in quantities more or less minute, these 

 substances, by combining with a portion of the liberated hydrogen, form compounds 

 whicli have strong and characteristic odours, and, though in small quantity, con- 

 tribute to the general effect. Of the hydrocarbons produced, the greater part 

 consists of members of the paraffin series ; but these are accompanied by more or less 



