Cht Popular ^cicnct 0tXaB 
AND 
BOSTON JOURNAL OF CHEMISTRY. 
Volume XXV. 
BOSTOK, JULY, 1891. 
]!^UMBER 7. 
I CONTENTS. 
Famimar Science.— Forms of Beauty— Co- 
hesion Figures 9.5 
Compressed Air 96 
An Ancient Irrigating Machine .... 97 
; Chlorine 9" 
ITie Nature of Solution '.' 
The Alleged Worth of Aluminium . . . \j. 
Preparation of the (Jxides of the Karer 
Elements 99 
Scientific Brevities 99 
The Out-Dook World. — An Interesting 
Convention 100 
Convention Notes 100 
A. A. Corresponding Geological Chapter . 100 
Wilson Ornithological Chapter .... 100 
Our Friends in IJussia 100 
Notes from Halifax 100 
The Agassiz Association Saved Her ... 101 
A Few Notes in Regard to Cats . . . . 101 
Vitality of Blackbird's Eggs 101 
A Geological Ramble 101 
Some Georgia INlinerals 101 
White Cardinal-Flowers 101 
The A. A. Lessons in Miaeralogy . . . 101 
The Microscope Prize 102 
A Squirrel's Unusual Meal 102 
List of the Plants of the District of Mos- 
chaisk, Government of Moscow, Russia . 102 
Editorial.— 'ae Manchots of the Cape of 
Good Hope 104 
.The End of the World 104 
Studies in Plant Biology 10.5 
Meteorology for May, 1891, with Review 
of the Spring 10.5 
.\stronomical Phenomena for July, 1891 . 106 
(Questions and Answers 106 
Literary Notes •. . 106 
Meijicink and Pharmacy.- 'I'he Mysteries 
of Contagion 107 
The Teeth in Relation to Health .... 107 
Monthly Summary of Medical Progress . 108 
Cure by Miracle 110 
Medical Miscellany 110 
I'LBLisiiERs' Column 110 
familiar iS@iei?ee. 
[OrlglDal In Popular Science News.] 
FORMS OF BEAUTY— COHESION FIGURES. 
BY E. RATTENBUKY HODGES. 
Various remarkable pheuomena are found more 
or less directly associated with, and sometimes 
owe their origin to, the surface tension of liquids. 
In our last article, entitled "Forms of Beauty," 
we attempted to desci-ibe the very striking changes 
which a drop of a solution of some coloring mat- 
ter or other substance exhibits as it descends and 
diffuses through another medium, such as water, 
oil, alcohol, etc. 
It is a matter of almost common observation 
that the film of a soap-bubble is in a state of 
strain. This is equally true of the surface of 
water or any other liquid contained within a ves- 
sel. If, now, we take up ou a clean glass rod a 
drop of SI line oil or other hydro-carbon, and 
gently deliver it to the surface of pure water in a 
properly cleansed dish or other suitable vessel, we 
shall probal)ly witness a most iiitcri^sling contest. 
The water surface in clinging to the oil will tend 
to spread it_out, since the adhesive force of the 
water^here comes interplay. On the other hand, 
the tendency of the oil-drop particles is to keep 
together, or cohere. Hence we shall see the beau- 
tiful phenomena which mark the struggle between 
cohesion and adhesion. 
But we must observe the conditions necessary 
o success with these experiments. Distilled 
.vater may be used, but rain or ordinary drinking 
water will suffice. The containing vessel must be 
chemically clean, (catharised), for the slightest 
trace of grease or other impurities would be fatal. 
I'he glass or "dish used for these experiments 
should be well rinsed with a solution of potash or 
common washing soda; then a sufficient quantity 
— say six or eight ounces — of water taken, other- 
wise it would be too soon saturated with the sub- 
stance under examination. The fingers must not 
touch the inside of the cleaned glass nor the sur- 
face of the water which it contains, because they 
would impart au organic film. The necessity for 
this precaution is strikingly proved by the fact 
that when small pieces of camphor are dropped 
on fresh water, they immediately spin about like 
water beetles, but the instant we touch the water 
surface with the finger they stop as if struck 
dead, — nor will they recommence their gyrations 
until the surface is again clean. Then, too, in 
order to see the effects about to be desciibed, one 
must not look down vertically at the (h-op, but 
obliquely, so that the entire water surface is re- 
flected to the eye. 
;a.^ 
H 
The above conditions having been complied 
with, if a drop of creosote is now delivered from 
a glass rod to the water surface, the drop will be 
seen to act in a remarkable way. It flattens out 
as a disk, having a silvery reflection, ami sails 
about with some speed, being also rapidly agi- 
tated with a motion that gives it the appearance 
of a living creature. (Fig. 1). " Its edge vibrates 
with rapid crispations : it darts out small globules, 
which immediately begin a series of motions of 
rotation and translation on their own account. 
In the mean tiiae, a silvery film spreads over the 
surface of the water ; the parent globule and the 
smaller globules become less energetic ; they per- 
form a number of motions among themselves, 
moving about in circular or curved paths, care- 
fully avoiding each other.'' Sometimes the larger 
globules remain still and the smaller rotate in 
little lakes which they clear for themselves in the 
film, as if to disport in. When these globules 
have all dissolved, a second drop of creosote de- 
livered to the same surface shows far less activ- 
ity; moreover, a longer time elapses before it 
disappears. 
These surface forms have been named cohesion 
figures by Prof. Charles Tomlinson, F. R. S., of 
London, England, their discoverer and investi- 
gator. In one of his monographs he says of the 
cohesion figure: "It may l)e regarded as the re- 
sultant of the cohesive force of the substance, its 
density, and the adhesion of the surface on which 
it is placed. I believe that every independent 
liquid has its own cohesion figure. By an inde- 
pendent liquid I mean not a solution ; for in the 
solution of solids and licjuids cohesion has been 
already overcome. * * * The cohesion figures 
of li(iuids will be more or less permanent in the 
inverse ratio of the solubility of the substance." 
He furtlier remarks that an increase of tempera- 
ture quickens and exalts the phenomena shown 
by many of these films. And here it is necessary 
to say that in preparing this piipcr the writer is 
largely indebted to Mr. Tomlinson s memoirs, pub- 
lished in the Philosophical Magazine in the years 
1861, 18G4, and 1807. 
7if^ 
M- 
These surface figures are numerous and dis- 
tinctly characteristic of the substances employed, 
and may be used as tests for all such organic 
bodies. "The cohesion figure of carbolic acid 
appears to be a sort of exaggerated form of the 
creosote figure. The water seems to tear it to 
pieces ; the crispations are amazingly active, and 
the disk quickly breaks up and disappears." (Fig. 
2). While a drop of creosote lasts five minutes 
on a water surface, a drop of the acid endures 
but a few seconds. A drop of absolute alcohol 
(ethylic) flashes out as a circular disk ; its central 
parts seem to resemble the petals of a fiower, 
(Fig. 3), although the figure does not last longer 
than one or two seconds. Naphtha treated In this 
way yields a circular film, its inner circumference 
being lined by a double row of little bosses, the 
inner row being smaller and fainter than the 
other. (Fig. 4). 
Some of the essential oils furnish cohesion fig- 
ures of extraordinary beauty and elaborateness 
i. 
