160 



KNOWLEDGE 



[July, 1903. 



"MOLECULES AND HEAT."*-A CRITICISM. 



By Edwin Epser, a.r.c.sc, f.ph.s. 



As the result of experiments carried on for a number of 

 years, Mr. Hoveuden claims tliat molecules can easily be seen 

 "by tbe unaided eye. Notbiuj,' could well l)e more startling 

 than such a claim ; it is proposed to examine briefly the 

 grounds on which it is based. It may at once be said that 

 Mr. Hovendeu is perfectly honest in the statement of his 

 case, and some of his experiments are worth repeating. 

 Further, for an untrained observer, he sometimes notes the 

 essential conditions of a phenomenon with commendable 

 sagacity, although his exj^lanations, as will be shown, are 

 often of a very partial character. Personally, I have to thank 

 Mr. Hovenden for his courtesy in showing me a number 

 of his experiments, and explaining his views thereon. 



Let us take a thin glass flask partially filled with a liquid, 

 such as water, spirits of wine, &c., and focus the rays from 

 an arc lamp at a short distance above the surface of the 

 liquid. After gentle heating, a large number of small 

 spherical liodies are seen fltiatiug aliout in the space above 

 the liquid. Mr. Hovenden claims that these small spherical 

 bodies are molecules of the liquid ; lie further defines a water 

 molecule as a spherical body composed of a great numher 

 of atoms of oxygen and hydrogen in the proportion of one 

 of the former to two of the latter. At first sight, 

 therefore, it would appear that a water molecule, as defined 

 by Mr. Hovenden, is indistinguishable from a small drop 

 oi' water composed of a great number of the generally 

 accepted molecules, each comprising one atom of oxygen 

 and two atoms of hydrogen. Mr. Hovenden has, however, 

 been struck by the fact that whereas a small drop of water, 

 when cast up from the surface of the boiling liquid, is 

 seen to quickly fall back again, yet the small particles 

 mentioned above exhibit no observable tendency to 

 gravitate, bvit slowly circulate, iu swirls and eddies, in the 

 space above the liquid. The accepted explanation of this 

 depends on the fact that a gas or liquid exerts considerable 

 friction on very small particles, which are thus unable to 

 sink quickly ; for similar reasons, muddy water clears very 

 slowly when at rest, and more slowly still when in motion. 

 We mav, however, for the moment forget this, and consider 

 Mr. Hovenden's explanation, which is that the small 

 particles seen floating above the liquid were invisibly 

 small when within the liquid, but during heating they 

 absorbed the ether (which is supjjosed to be an aiiti- 

 gravitating fluid), and expanded to visible dimensions, at 

 the same time acquiring anti-gravitative properties. Mr. 

 Hovendeu has noticed that these particles are only to be 

 seen when there is cold air in the flask. To most observers 

 this would suggest that their jjresence demands conditions 

 favourable to condensation. Mr. Hovendeu, however, 

 proposes the explanation that, when cold air is not present, 

 the particles become invisible, just as finely-divided glass 

 particles, which form a white flour-like powder in air, 

 become almost invisible when mixed with water. When 

 the liquid is caused to boil, and air is expelled from the 

 flask by the vapour given off, the space above the liquid 

 appears absolutely empty. " Bui," says Mr. Hovenden, 

 " the flask is full of these spheres, for they issue out of 

 the flask as steam." This is begging the question. The 

 particles may truly be seen leaving the mouth of the 

 flask, but this is perfectly consistent with the orthodox 

 explanation that the interior of the flask is filled with 

 aqueous vapour, the invisibly small molecules of which are 

 comparatively widely separated from each other. At the 



* " On Eesolving the Molecule and Seeing It." " Wliat is Heat ? : 

 A Peep into Nature's Most Hidden Secrets." By Frederick Hovenden, 

 F.I..S., F.G.S., F.K.U.S. 



mouth of the flask the vapour mixes with the cold dust-laden 

 air of the room, and condenses into small water droplets. 



Mr. Hovenden also fills spirit lamps with various liquids 

 and concentrates the electric light on the wicks. In each 

 case a stream of small particles is seen rising from the 

 wick into the air, and these jiarticles are claimed to be 

 molecules. If the lamp is filled with methylated spirit, 

 the stream of particles leaving the wick becomes bright, 

 almost resembling a flame. This experiment is a very 

 pretty one, and might be found useful to teachers, as 

 showing the effects produced liy the absorption of radia- 

 tions. Mr. Hovenden's most striking experiment, how- 

 ever, consists in lighting the spirit lamp and placing the 

 flame in the focus of the elei-tric light. Particles, similar 

 to those formerly described, but much less numerous, are 

 seen in the interior of the flame, and Mr. Hovenden claims 

 that iu this case condensation is necessarily eliminated. 

 Careful examination shows that the particles are visible 

 only near the boundary between the luminous mantle 

 of the flame and the non-luminous central core. This 

 core is known to be cold, so that once more we have 

 the conditions that the particles are fonued only where the 

 heated vapours have the opportunity of becoming cooled. 

 It may be admitted that condensation occurring under the 

 above is somewhat surprising, and Mr. Hovenden's obser- 

 vation is certainly of considerable interest. 



I cannot see that Mr. Hovendeu has given us any 

 experimental proof that the particles seen in the above 

 experiments are molecules, and not small drojjlets of con- 

 densed liquid. To disprove the theory which he proposes, 

 it is only necessary to compai-e his fundamental conception 

 with the results of experiments. He considers that a solid 

 consists of invisibly small spherical molecules, iu contact 

 with each other. When the solid is heated, each molecule 

 absorbs "ether," and expands as a soap bubble does when 

 air is forced into it. This absorption of ether, and the 

 consequent expansion of each molecule is considered to be 

 essential to a rise of temperature. Of course such a theory 

 labours under all the difficulties that beset the old caloric 

 theory; indeed, writing "caloric" instead of "ether," in Mr. 

 Hovenden's theory, we go hack to the opinions of the early 

 part of the nineteenth century, and Davy's experiments 

 appear to disprove one as conclusively as the others. But 

 Mr. Hovenden's theory can be disproved on other grounds. 



If a rise of temperature is necessarily connected with an 

 expansion of the molecules of a body, then all substances 

 must expand when heited. Now a piece of glass rod, 

 when heated to redness, expands so much that, on plunging 

 it into cold water, it is shivered to fragments by the 

 sudden contraction. So far facts are in accordance with 

 Mr. Hovenden's theory. But a rod of fused (juartz (more 

 strictly speaking, fused silica) can be heated to a white 

 heat, and then plunged into liquid air without the slightest 

 danger, or any signs of an appreciable change of dimen- 

 sions occurring. It can scarcely be claimed that, during 

 these operations, the temperature of the fused silica does 

 not alter ; he it cert.iinly leaves the rod when it is plunged 

 into the liquid air, and causes the latter to boil violently. 

 On the other hand, experiment shows that during cooling, 

 a slight contraction which occurs at one stage is com- 

 pensated for by a slight expansion at another stage, so that 

 at th3 low temperature the dimensions of the rod are the 

 same as at the higher temperature. If the molecules are in 

 contact, it also follows that the dimensions of a molecule are 

 the same at the lowas at the high temperature. Thusachange 

 of dimensions does not always occur when a body is heated. 



If further evidence were needed, we might instance the 

 contraction of water as it is heated from 0"C. to 4'' C. 



Mr. Hovenden has further attempted to exjilain the heat 

 of chemical reactions in terms of his theory. When 



