452 



NA TURE 



[September 8, 1898 



caused by a small convection current which still was produced 

 in spite of these precautions. 



For, as suggested by Dr. Ramsay several years ago, a sub- 

 stance must have a molecular weight at least fifteen times that 

 of hydrogen to produce a sensation of smell at all, and, further, 

 since camphor, with which many of my experiments have been 

 made, has, when vaporised, a density about five times that of 

 the air, it seems unlikely that scent vapour should diffuse much 

 more quickly upwards through a vertical column of air than 

 through a horizontal one. At the same time, not only are the 

 tests with the glass tubes very striking, but the general impres- 

 sion which exists that smells rise, indeed the very fact that the 

 nasal channels of animals open downwards, tends to show that, 

 whether due to draughts or not, smells have really a tendency 

 to ascend. And the following result obtained with glass tubes 

 closed at one end with stoppers carrying respectively 

 camphor, menthol, oil of limes, &c., and at the other 

 end with corks, is instructive on this point. For, on un- 

 corking such a tube after it had been closed for a long time and 

 allowing the odour to stream out of it through the open air 

 towards the experimenter's face, it was always found that the 

 tube had to be brought much closer when the scent stream was 

 poured downwards than when she was in a vertical position and 

 It was allowed to ascend, although, when it was poured down- 

 wards, the experimenter brought her nose into as favourable a 

 position as possible for receiving the smell, by lying down with 

 her head thrown well back. 



As an illustration of the inefficiency of diffusion alone to 

 convey a smell you will find that if you hold your breath, with- 

 out in any way closing your nose either externally or by con- 

 tracting the nasal muscles, you will experience no smelling 

 sensation even when the nose is held close to pepper, or a strong 

 solution of ammonia, or even when camphor on a minute tube 

 is introduced high up into the nostril. Mere diff"usion from the 

 lower nasal cavity into the upper cannot apparently take place 

 with sufficient ease to produce the sense of smell, so that an 

 actual stream of air through the upper portion of the nose seems 

 necessary even when the nose is a very sensitive one. This 

 stream, for substances placed outside the nose, is produced by 

 breathing m, no smell being detected while breathing out. On 

 the other hand, if a substance be placed inside the mouth its 

 flavour is recognised when the air is forced outwards through the 

 nostrils — that is, at each expiration. Hence we may experience 

 alternately two totally different smells by placing one substance 

 outside the nose and the other in the mouth, the one smell being 

 noticed in inhaling and the other in exhaling. And the latter 

 can be increased by smacking the lips, which, I think, has really 

 for its object the forcing of more air through the nostrils at each 

 expiration. 



Experiments on the propagation of smells in a vacuum have 

 also been commenced in my laboratory, and the results are no 

 less surprising than those obtained with the propagation in air. 

 A U tube, seven inches high, had the odoriferous substance 

 placed inside it at the top of one limb, and a very good vacuum 

 could be made by allowing mercury to flow out of the tube. 

 Then the two limbs were separated by raising the mercury 

 column, and air being admitted at the top of the other limb, 

 without its coming into contact with the odoriferous substance, 

 the nose was applied at the top of this limb. 



When liquids like ammoniated lavender, smelling salts, solu- 

 tion of musk, and amyl acetate were employed, and various 

 devices were used for introducing the liquid, and preventing its 

 splashing when it boiled on exhausting the air, it was found 

 that the time that it was necessary to leave the two limbs con- 

 nected for a smell to be just observable was reduced from a few 

 minutes or seconds when the tube was filled with air to less than 

 half a second for a good vacuum ; with solid camphor it was 

 reduced from twenty minutes to one second, and when moist rose 

 leaves were used, from fifty minutes to two seconds. But with solid 

 particles of musk the time was not reduced below twenty minutes 

 by taking away the air, while with dried lavender flowers and 

 dried woodruff leaves no smell could be detected after the two 

 limbs had been connected for many hours, and a good vacuum 

 maintained. These experiments are, of course, somewhat com- 

 plicated by variations in the amount of odorous surface exposed, 

 but they seem to indicate that with these particular dried sub- 

 stances either the rate of evolution of the scent, or its rate of 

 propagation, or both, are very slow even in a good vacuum. 



I have also carried out some tests on the power of different 

 substances to absorb various scents from the air. Lard, it is 



NO. 1506, VOL. 58] 



well known, is used to absorb the perfume from flowers in the 

 commercial manufacture of scents, perhaps because it has little 

 odour of its own, and because the scent can be easily distilled 

 from it. But if lard, wool, linen, blotting-paper, silk, &c., be 

 shut up for some hours in a box at equal distances from jasmine 

 flowers, dried woodruff leaves, or from a solution of ammonia, I 

 find that it is not the lard, but the blotting-paper, that smells 

 most strongly when the articles are removed from the box. On 

 the other hand, when solid natural musk is employed, it is the 

 wool that alone acquires much smell, even after the box has 

 been shut up for days. 



Another noteworthy fact is the comparatively rapid rate at 

 which grains of natural musk are found to lose their fragrance 

 when exposed to the air. The popular statement, therefore, 

 that a grain of musk will scent a room for years supplies but 

 another example of the contrast between text book information 

 and laboratory experience. 



The power of a smell to cling to a substance seems to depend 

 neither on the intensity of the smell nor on the ease with which 

 it travels through a closed space. Musk has but a faint smell, 

 but the recollection of the greeting of a rich Oriental survives 

 many washings of the hands. The smell of rose leaves, again, 

 is but faint, and it travels very slowly through air in a tube ; and 

 yet the experiments on its propagation in the glass vacuum ap- 

 paratus were rendered extremely troublesome, by the difficulty 

 experienced in removing the traces of the smell from the glass 

 between the successive tests. Rubbing its surface was quite in- 

 effectual, and even the mercury had to be occasionally shaken 

 up with alcohol to free it from the remanent smell. In fact we 

 found, as Moore put it : 



" You may break, you may shatter the vase if you will, 

 But the scent of the roses will cling to it still." 



This absorption of scents by glass, and the ease with which I 

 found that jasmine flowers could be distinguished from woodruff 

 leaves, even when each was enclosed in a series of three enve- 

 lopes specially prepared from glazed paper, and when many 

 precautions were taken to prevent an odour being given to any 

 of the envelopes in the operation of closing, as well as to pre- 

 vent its diffusion through the joints in the paper, led me to try 

 whether an actual transpiration through glass could be detected 

 with the nose. For this object a nnmber of extremely thin glass 

 bulbs were blown from soda and from lead glass, so thin that 

 they exhibited colours like a soap bubble, and felt, when gently 

 touched, like very thin oiled silk, and after a little ammoniated 

 lavender, amyl nitrite, ethyl, sulphide, mercaptan, solution of 

 musk, oil of peppermint, and propylamine had been introduced 

 into them respectively, they were hermetically sealed, and placed 

 separately in glass stoppered bottles. 



In some cases, on removing the stopper from a bottle after 

 many hours, a faint odour could be detected, but so, generally, 

 could a minute flaw after much searching ; the crack, however, 

 being so slight that it did not allow sufficient passage of the air 

 to prevent the bulb subsequently breaking, presumably from 

 changes of atmospheric pressure. And in those cases where a 

 smell was detected without any flaw being found in the glass, 

 the subsequent breaking of the bulb put an end to further test- 

 ing. The question therefore remains unanswered. 



In presenting this brief introduction to the physics of smell, 

 I have aimed at indicating the vast territory that waits to be 

 explored. That it will be found to contain mines of theoretical 

 wealth there can be no doubt ; while it is probable that a 

 luxuriant growth of technical application would spring up later 

 on. Already, for example, Mrs. Ayrton unintentionally picks 

 out inferior glass by the repugnance she shows at drinking water 

 out of certain cheap tumblers. To conclude, I may say that 

 one of my fondest hopes is that an inquiry into the physics of 

 smell may add another to the list of wide regions of knowledge 

 opened up by the theoretical physicist in his search for answers 

 to the questions of the technical man. 



S E C T I O N B. 



CHEMISTRY. 



Opening Address by Prof. F. R. Japp, M.A., LL.D., 



F.R.S., President of the Section. 



Stereochemistry and Vitalism. 



Of the numerous weighty discoveries which science owes to 



the genius of Pasteur, none appeals more strongly to chemists 



than that with which he opened his career as an investigator — 



the establishing of the connection between optical activity and 



