96 
POPULAE SCIENCE ITEWS. 
[July, 1891. 
Pure olive oil gives a finely iridescent film with 
an indented edge, whicli shortly changes to some- 
thing very lilie a lace pattern. A portion of the 
film at this stage is represented hy Fig. 5. In a 
few minutes this pattern vanishes, and the oil 
collects in irregular lines with ragged edges, sur- 
rounded by many small globules. A drop of oil 
of almonds yields a large fllra, also with a beauti- 
ful lace-like edge, (Fig. G), which soon disappears 
by the holes opening into each otlier. Soon the 
edge brealis away from the parent film and forms 
small lenticules outside it. The edge of the film 
appears raised; its holes continue to open and 
widen, and the detached portions shrink to lenti- 
cules. In a few minutes the parent film lias 
diminished to about tlie size of a qusirter piece, 
and is seen surrounded by numbers of lenticules 
of various degrees of minuteness. In the case of 
oil of peppermint, the drop, when placed on water, 
spreads and develops "a honey-combed Ulra," 
displaying color. The oils of turpentine, cinna- 
mon, anise-seed, etc., each yield finely character- 
istic cohesion figures. 
Newly distilled oil of coriander gives a beautiful 
figure. The edge of the film becomes deeply ser- 
rated, and a double row of lenticules surround it. 
Presently some of the indentations run in and 
then branch out as rounded lioUows of almost 
tree-like outline, within the disk. The slietch 
(Fig. 7) represents this second phase. Colza oil 
forms a large, smootli film, with iridescent rings, 
which immediately disappear. Minute lioles open 
at the edge at intervals, three or four together, — • 
sharp and clean, as if punched out. Similar per- 
forations form in other parts of the film, and 
In one" case it was found that if a drop of strong 
sulphuric acid be delivered to the surface of clean 
mercury, characteristic phenomena result. The 
drop of acid instantly spreads and covers the mer- 
cury ; but cohesion immediatelj' begins to reassert 
its claims, and forms the acid near the edge into 
large, flat bosses, each of which becomes a center 
of action ; minute globules pass in and out of it ; 
similar ones move to and fro over the rounded 
edge of the mercury. After a few minutes all 
action ceases ; the film contracts witli a smootli 
surface and well defined edge. Then, too, it was 
observed that a drop of alcohol or ether held over 
tlie acid film when at its widest, instantly gathers 
it up into a small disk — there being a much 
stronger adhesion Ijetween the acid and the alco- 
hol or ether vapor than between the acid and the 
metal. 
these widen and thicken at the edges until the 
surface acquires a honey-combed pattern, the 
holes pressing together in twos and threes. These 
large holes with thickened edg^s, grouped to- 
gether, are characteristic of the colza film. Mr. 
Tomlinson thus graphically describes the behavior 
of a drop of oil of lavender on water: "The ad- 
hesion of the water will cause it to spread out 
into a film; but the cohesion of the oil immed 
ately begins to reassert itself ; the film opens in a 
number of places, forming long, irregular arms, 
or processes, resembling the pattern assumed by 
worm-eaten wood. These processes tend to gather 
up into separate disks or lenticules ; the adhesion 
of the water spreads them out, and the cohesion 
of the oil struggles to prevent this, and soon pre- 
vails; the almost immediate issue being the 
formation of the original drop into a number of 
disks, with sharp, well-<leflned outlines and con- 
vex surfaces." 
By varying the surface, the phenomena ex- 
hibited by the drop under examination were found 
to likewise vary in many ways. Tomlinson's ex- 
periments in this direction were published by him 
in 1864. We can here only mention some of the 
substances used. Instead of water surfaces he 
employed those of cocoa-nut oil at 80° F., of cas- 
tor oil at aiiout 90° F., paraffin, spermaceti, wax, 
and lard made fluid at various temperatures, sul- 
pliur made liquid l>y lieat, and also olive oil. He 
states that "some of the figures formed on these 
surfaces are very remarkable and of great beauty." 
In June, 1867, this able scientist published an 
account of results he had obtained in the course 
of investigations on "the cohesion of liquids to 
liquids and tlie displacing power one liquid has 
over another." I cannot do better than give one 
extract from that most interesting monograph. 
It is also a good example of the author's descrip- 
tive power, which, by the way, is always gov- 
erned by love of scientific accuracy. "Many of 
the oils of the tui-pentine series spread with energy 
on the surface of water, llius a drop of the es- 
sential oil of turpentine no sooner touches the 
surface tlian it flashes out into a film. If, now, a 
drop of creosote be placed on this film, it simply 
slips through and falls to the bottom of the ves- 
sel ; but if the drop be carefully delivered to the 
water near the edge, it will form a convex lens, 
and, slightly repelling the turpentine film, make 
its way into it, so as to be surrounded by it, witJi 
a clear intervening space. In the mean time the 
turpentine becomes thinner by evaporation and 
displays its iridescent colors. The creosote lens 
flattens, widens the clear space around it ; soon 
the edge begins to quiver ; and all at once, as if at 
a signal, the vibrations suddenly set in, the figure 
sails about, everywhere repelling the film, and 
causing it, or what is left of it, to gather up into 
disks. When the creosote figure has disappeared, 
the turpentine disks begin slowly and cautiously 
to flatten out into films. A second drop of creo- 
sote will cause them instantly to collapse. A 
second drop of turpentine will, in like manner, 
shut up into a lens the second creosote figure. 
The film goes through its changes as before ; the 
second creosote figure in due time becomes active, 
and when it has disappeared the disks of turpen- 
tine flatten out as before." The action of a creo- 
sote drop near to an oil of cajeput film on water is 
also most curious, and receives an equally graphic 
description. If a small sponge fastened to one 
end of a glass rod be dipped in benzine and 
brought near to a creosote drop floating on water, 
the benzine vapor has a powerful repulsive action 
on the drop, so that it spreads and then splits up 
with a kind of jerking motion. The vapor of car- 
bon disulphide also has a powerful ett'ect on a 
similar drop. In certain states of saturation of 
the water, a drop of benzol is so exceediugly 
active that it pursues the creosote and attacks it 
witli life-like motions, while the latter darts about 
as if trying to escape from its adversary. 
These cohesion figures furnish good physical 
tests for any given substance. As the pure oil, 
spirit, etc., yields its own proper cohesion figure, 
any departure from the standard figure is sug- 
gestive of impurities or adulteration, altliough 
sometimes ciiemical changes (due to long keep- 
ing, exposure to light, air, or extremes of temper- 
ature) are the cause of variation. It is greatly to 
be regretted that, so far, no illustrated catalogue 
of such figures has been produced. Instantaneous 
photography, aided by polarized light, may yet 
secure this very desirable object. About twenty 
years ago, Professor Woodward, of Manchester, 
England, devised an instrument by whicli some 
cohesion figures could be reflected on to a screen 
and exhibited to a large audience. But many 
films are too delicate to serve for exliibiting liy 
optical apparatus ; they are simply drowned in a 
flood of light. A lady pharmacist in the United 
States obtained some of these figures on paper; 
these were termed oleographs, but her results were 
hardly more successful tlian those of Dr. MoflTat. 
Doubtless many new coliesion figures will be dis- 
covered when a yet more extensive series of in- 
vestigations are made with drops and surfaces of 
all kinds and under various temperatures and 
pressm-es. ^_ 
[Original In Popular Science News.] 
COMPRESSED AIK. 
BY HEKBEUT S. ROBINSON. 
There are but few people who know tliat the 
air we breathe, when compressed, is used in many 
large factories, foundries, and machine-shops all 
over the world, to do work of different kinds for- 
merly done by hand. And yet such is the case, 
and, when you have once thought sucli a thing 
possible, it seems no more wonderful than the 
telegrapli, phonograph, and other recent develop- 
ments of electricity. 
Take, for example, the putty-blower which the 
mischievous schoolboy uses. The air is, to a cer- 
tain extent, compressed before it forces out the 
wad of putty or paper. It therefore seems prac- 
ticable to compress it and confine it, subject to 
the uses to which it is to be put. A somewhat 
modern device, which is much used in large public 
buildings, theatres, etc., is a fan. In winter warm 
air can be fanned througli the flues to registers 
all over the house, thus doing away with the un- 
sightly radiator. In summer the same fan can 
be used to force cool, fresh air to every room. I 
recently examined a large plant of this kind, 
which was a very complete one. On one side of a 
small room was the fan— a huge affair, eleven feet 
in diameter and about three feet in widtli. It was 
run by a small engine at the rate of about one 
