PREPARATION OF SOAP FOR SOAP LINIMENT. 
415 
of molecular constitution are boiling-points. Whenever truly analogous ele¬ 
ments are comparable in respect to boiling-points, it is found that those com¬ 
posed of heavier atoms boil at higher temperatures than those composed of 
lighter atoms. A comparison of the successive terms of the series—chlorine, 
bromine, and iodine—illustrates this difference very strikingly. So, also, a 
comparison of the several terms of the series,—oxygen, sulphur, selenium, and 
tellurium, and, not less so, the elements, nitrogen, phosphorus, arsenic, anti¬ 
mony, aud bismuth. 
“ Now, whenever volatile organic compounds belonging to a homologous series 
are compared, it is found that, of two such compounds, the one having the 
higher molecular weight has also the higher boiling-point. The glycols present, 
however, an exception to this general observation. 
“ The melting-points of homologous organic compounds also show differences 
running parallel in like manner to their differences of molecular weight. 
“ The relative velocities of motion of particles, as shown by the processes of 
diffusion, afford another confirmation of the general truth of the molecular 
weights ; for, on the one hand, it is known that heavy particles diffuse more 
slowly than light particles ; on the other hand, a comparison of the relative ve¬ 
locities of movement of molecules of relative weights, previously determined 
upon chemical evidence, shows that the heavier molecule of chemistry is also 
the heavier molecule in diffusion. 
“Among chemical evidences of atoms the discovery of the distinction between 
direct and indirect combination is worth consideration, more especially as it is 
independent of the quantitative comparisons which have hitherto guided us. 
Many elements which have never been obtained directly combined, are bound 
together by a third ; thus we have no direct compound of hydrogen and potas¬ 
sium, but in potassic hydrate an atom of hydrogen is united with oxygen, and 
an atom of potassium is united with this same oxygen, HOK. Hydrogen in 
this hydrate is indirectly united with potassium, an atom of oxygen being the 
connecting link between them. . x 
u What concerns us in these reactions is to see the evidence which they afford 
that the binding element is an atom. The very fact itself amounts to that. 
In potassic hydrate, oxygen is combined with hydrogen ; it is also combined 
with potassium, but the hydrogen cannot pass off, even at a red heat, in combi¬ 
nation with its half of the oxygen. The two halves are inseparable, and when 
I say that in the molecule of potassic hydrate there is a single atom of oxygen, 
I merely state that fact.”* 
(To be continued.J 
THE PREPARATION OF SOAP FOR SOAP LINIMENT. 
BY C. II. WOOD, F.C.S. 
The process given in the British Pharmacopoeia for the preparation of lini- 
mentum saponis is, I believe, founded upon the results of some experiments 
communicated to the Society by Mr. Deane in lb59. Mr. Deane found that 
when good Castile soap is macerated in the spirit at a temperature below I., 
the oleate of soda dissolves, while the margarate of soda remains to a great 
extent insoluble, and the resulting solution does not lose its limpidity by the 
application of moderate cold. If, on the contrary, the whole of the soap be 
* Williamson on the Atomic Theory, Journ. Chem. Soc., ser. 2, vol. vii. p. 328. 
