162 
POPULAE SCIENCE NEWS. 
[November, 1891 . 
[Original In Populab Science News.] 
SETTLING A QUARREL BY FLUOKES- 
CEINE. 
Br WILLIAM BERNHAKDT. 
A REMARKABLE addition to the vast and con- 
tinually increasing number of applications whicli 
chemistry has found in practical life is reported 
from Germany. The event is the more striliing 
by giving evidence of the incredible sensibility 
sometimes observed in chemical reactions. 
In a mountainous part of the above-mentioned 
country, located at the watershed of two large 
streams, the population from ancient times en- 
joyed an abundance of delicious trout frequenting 
the environing brooks. Modern industry, how- 
ever, did not hesitate to place several manufacto- 
ries on the shores of these creeks, and their refuse 
waters soon were noticed to pollute the downward 
courses. The raisers and consumers of fish, how- 
ever, were soon to protest ; they sued one of these 
establishments for damages, claiming that the 
refuse fluids had killed all the fish in their brooks. 
To this the manufacturer objected, declaring there 
was no communication between the water passing 
his works and the plaintiffs' brooks. The latter, 
however, though no visible connection of both 
waters could be ascertained, maintained that the 
communication was a subterranean one. 
This being the state of afi'airs, a chemist hap- 
pened to visit the scene of the quarrel, and, hav- 
ing been informed about the trouble, at once de- 
clared that the question might very easily be 
settled by a simple optical test. Both parties 
agreeing to submit to his decision as an expert, 
he undertook to perform the task. 
The class of organic compounds comprised by 
the name of benzene derivatives, and abounding 
with brightly and richly colored bodies, as well 
as with important medicines, also includes a sub- 
stance called " fluoresceine,"' from the peculiar 
intense fluorescent properties of itself and some 
of its compounds. The substance represents a 
dark red powder, dissolving in alcohol with a red- 
dish color having a green fluorescence. Its com- 
pound with sodium oft'ers this green fluorescence 
to an almost incredible degree of intensity ; it is 
perceivable in water containing one part of the 
compound to ten millions of water. In its effect 
upon man and animals of any kind, however, 
fluoresceine is a perfectly harmless substance. 
It was to the optical property of fluoresceine 
that our expert resorted when one flue day, pro- 
vided with a tin box containing two pounds of the 
sodium compound, he proceeded to dissolve it in a 
barrel of water, the contents then being poured 
into the brook above the factory buildings. No 
sooner had the admixture taken place than the 
brook, formerly clear and transparent, became 
opaque, but of a shining green color, which 
spread rapidly downward with the flowing water. 
All the water in the lower course of the brook, 
and even In some ditches and creeks which had 
not been known to communicate with the brook 
subjected to the test, became green, and kept this 
color unto its inflow into the broad stream about 
five miles away. 
The population were astonished and became ex- 
cited, fancying that the water had been poisoned 
—a fear which they did not abandon before hav- 
ing been convinced that the water was still drink- 
able and unchanged in taste, and even in color 
when held against the sun. The green hue was 
only perceived in the water covering the dark 
background of the river bed. People also became 
easily persuaded that only the water in communi- 
cation with the stream passing the factory was 
subject to the change, all the others having re- 
mained in their former condition, including the 
one belonging to the suing fishermen, who there- 
upon gave up tlie complaint and resorted to effi- 
cient expedients to provide fresh trout for their 
waters. 
The question whether there are communications 
existing between several natui-al currents of water 
may happen to be both of scientific and practical 
interest. The recent formation of a lake near the 
Colorado River gave rise to various conjectures as 
to its origin. In such cases the fluoresceine test 
would answer with unsurpassed certainty. It 
would also reveal the source of pollutions in 
drinking-water in the researches that are at pres- 
ent being performed in the Croton district, sup- 
plying the city of New York. 
SCIENTIFIC RECREATIONS. 
Two interesting experiments in centrifugal 
force are illustrated in the accompanying engrav- 
ings. To perform the first experiment, take a 
sojip-plate and place a napkin-ring exactly in the 
center (Fig. 1). Then, holding the plate in the 
Fig. 1. 
two hands by its opposite edges, toss it into the 
air with a quick revolving motion so that it shall 
make a complete turn before being caught. The 
centrifugal force developed by the revolution of 
Fig. 2. 
the plate will hold the napkin-ring in its place as 
firml}' as if it was glued there, and plate and ring 
will return to the hands of the experimenter in 
he same relative positions with which they 
started. The experiment may be varied by plac- 
ing the ring at the edge of the plate, outside the 
axis of rotation, when it will invariably fly off 
from the plate wlien thrown into the air. The 
first trials of this experiment are likely to be fail- 
ures, but the necessary skill is quickly obtained 
by a little practice. 
Another beautiful illustration of centrifugal 
force can be shown by attaching a light metallic 
chain to a piece of string about a foot long (Fig. 
2, A). On twisting the string so as to cause the 
chain to revolve rapidly, it will rise to a hoiizontal 
position, open out into a ring, and revolve in a 
circle with the supporting cord, giving the appear- 
ance shown in Fig. 2, B. If the chain cannot be 
obtained, a loop of heavy cord, or even a pencil 
suspended by one end, will answer almost as well. 
In a late number of La Nature — from which, 
also, the preceding engravings are taken — ^we find 
an additional example of the possibilities of pho- 
tography with a non-actinic background, (described 
in the October number of the Science News), 
which is such an excellent one that we reproduce 
it for the benefit of our readers. In this pictiu'e 
the little girl with the cart was first photographed, 
and then the boy was placed in position against 
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the dark background formed by the open door of 
the building, and his head focussed upon the 
ground glass so that it apparently occupied a 
position in the cart, as shown in the engraving. 
A piece of black cardboard pierced with a hole of 
the proper size was placed before the lens dui-ing 
the second exposure, which cut oft" all the rays of 
light excei)t those proceeding from the head and 
shoulders of the model, and allowed those only to 
be impressed upon the plate. 
SOME CONVENIENT FORMS OF KNOTS. 
The accompanying engravings illustrate the 
various ways in wliich a rope may be quickly and 
firmly attached to objects of varying size and 
weight, and are almost self-explanatory. The 
knot represented in Fig. 1 is firm enough for a 
light stick of timber or similar object, while 2, 3, 
or 4 can be used where a stronger fastening is 
required. Figs. 5 and 6 show two convenient 
