676 report — 1884. 



and ammonium carbonate, which cannot exist at all in the gaseous state, the 

 temperatures of volatilisation do not form a curve. When the dissociation was 

 considerable but not complete, as in the case of phthalic and succinic acids, an 

 indication of a curve was observed at low pressures, but it differed widely both in 

 form and position from that representing the vapour pressures or pressures of 

 dissociation. As the dissociation decreases the curves approach each other more 

 closely, and they appear to be coincident in the case of ammonium chloride and. 

 nitric peroxide within the limits of temperature at which observations were made,, 

 and at which the amount of dissociation is probably small. With acetic acid J 

 very numerous observations proved the perfect coincidence of the curves. 



The results appear to be unfavourable to the view that when liquefaction of a 

 gaseous stable substance takes place, gaseous molecules coalesce to form more 

 complex groups of molecules, and that these complex molecules dissociate when the 

 substance is vaporised. 



5, On Molecular Volumes. By Professor William Ramsay, Ph.D. 



1 . The object of this research was to ascertain whether, as has been long taken 

 for granted, the boiling-points of compounds under equal pressures really afford 

 suitable points for a comparison of their molecular volumes. The experiments 

 described in detail in the original paper were made during the years 1880 and 1881, 

 and a preliminary notice was read to the Chemical Society in the spring of that 

 year. An account of experiments by W. Staedel appeared subsequently, in which 

 he showed that the element chlorine possesses at least three different volumes in 

 combination. Subsequent researches by Lossen, Schiff, and others have since that 

 time thoroughly proved that no element enters into combination with invariable 

 atomic volume. The experiments made by the author decisively prove that in the 

 following series of compounds: water, methyl alcohol, ethyl alcohol, propyl 

 alcohol, isopropyl alcohol, isobutyl alcohol, and ether; the value of the group CH 2 

 is by no means constant, while at the boiling-points of the liquids at low pressures 

 the value is approximately constant, fluctuating between 175 and 22 ; at high 

 temperatures the difference becomes much more apparent, attaining, at pressures of 

 20,000 mins. (which was the highest measured), the greatest irregularity. Thus 

 the difference between the molecular volumes of ether and isobutyl alcohol, two 

 isomeric substances, amounts to a total of about 20 units, whereas the hypothesis 

 that at the boiling-points under equal pressures the molecular volumes are com- 

 parable, and for isomeric substances should be equal, no difference between these 

 substances should be observable. 



2. It was supposed that as liquids at high temperatures corresponding to high 

 pressures are extremely compressible, the volumes might be comparable, provided 

 they were compared under critical pressure ; the temperatures, however, at which 

 they were compared still being those at which their vapours exert equal pressure. 

 To elucidate this point, careful measurements of the compressibility of these liquids 

 were made, and also of their critical temperatures and pressures, and it was found 

 that when the liquids w T ere at the temperatures corresponding to equal vapour 

 pressure, but exposed to their critical pressures, no correspondence between their 

 molecular volumes was observable. 



3. As a last alternative it was thought possible that if the liquids still at 

 temperatures corresponding to equal vapour pressures, could have existed under 

 no pressure, some basis of comparison might be found. Necessarily such a state is 

 unrealisable in practice, but as the compressibility of the liquids had been deter- 

 mined, it was calculable. Again, it was found that in this hypothetical condition, 

 although the relative volumes at high temperatures were considerably altered, yet 

 no point of comparison had been reached. 



4. The author therefore concludes that, contrary to what has usually been 

 supposed, the boiling-points of liquids under whatever pressure they may be taken 

 are not suitable temperatures at which to compare their molecular volumes. 



Still it cannot be denied that a certain regularity is noticeable. Th*- 

 approximate constancy of the atomic volumes of elements which is made by Kopp 



