Vol. XXV. No. 4.] 
POPULAE SCIENCE ITEWS. 
51 
one of the members stated that he had a little 
heater in his house which the laundress at any 
time connected up with one of tlie incandescent 
lamp sockets, and by means of which she ironed 
all day, the iron getting only so hot and never 
any hotter. Cooking is very often done in this 
waj' also now, and with the general extension of 
lighting circuits we may look for an enormous 
number of inventions in apparatus for using elec- 
tric heat in the familj'. The change will go even 
turtlier than this, for if heat can be brought into 
an office or a house through the agency of a small 
wire, there is certainly no need to convert the 
cellar of every house into a miniature coal mine, 
with all the attendant nuisance of running a fur- 
nace or open fires and then getting rid of the 
asiies. It is quite within the bounds of possibility 
that at no distant day our heat will be gently ra- 
diated for us from the wall paper, and light sup- 
plied to us from a luminescent ceiling, — and all by 
the simple pushing of a small button in some ob- 
scure corner of the room. 
[Original in PoPULAK SCIENCE News.] 
TIIE GINSEXG FAMILY. 
BY S. E. KENNEDY. 
Eakly in May we find the pretty white blos- 
soms of the little plant known as dwarf ginseng. 
It is often in company with the anemone, and its 
whorl of three palmately compound leaves rather 
suggests that flower ; but, upon examination, one 
soon decides that the specimen belongs to the 
rather limited order of araliads. The root, which 
is somewhat keen to the taste, is found deeply 
imbedded in the earth and attached to the stem by 
a short ligament. It is small and round, which 
perhaps suggested its other common name of 
■'ground-nut." Local names are of but little real 
use, and yet one would scarcely be willing to call 
this tiny i)lant Aralia trifolia every time he wished 
to speak of it. It would not be a bad plan, how- 
ever. This species grows from six to nine inches 
high, the simple stem terminating in a peduncle 
which bears the umbel. Its perfect and imperfect 
flowers are borne on different plants. 
The root of A. quinqiiefolia is large and fleshy, 
sometimes nearly a foot in length, spindle-shaped 
and often forked. It is in some repute as a drug, 
1 believe. This, too, has a smooth, round stem, 
with a terminal whorl of three compound leaves 
with five leaflets, and a central peduncle bearing 
an umbel of yellowish flowers. Although some- 
what familiar with this species from specimens 
ol)tained from a distance, I have never seen it 
growing, and do not think it is here; but the 
smaller kind grows plentifully, and is mucTi prized 
because it blooms so early. 
We have the A. nudicanlis, which, I suppose, is 
very common. The pleasure of lifting its long 
horizontal roots from the ground is one of the 
chief attractions of a spring ramble in the woods. 
The bright sunshine, the soft, warm winds, the 
pleasant smell of "the green things growing," 
take one back to tlie days of childhood, when, 
content with simple pleasures, we gathered the 
large shining leaves of this plant and ciilled them 
our "umbrellas." The wild sarsaparilla, as it is 
sometimes called, has no proper stem, l)ut a short 
scape, which bears the three umbels of greenish 
flowers. Tills was of great repute in our grand- 
mothers' day, as being one of the ingredients in 
the spring medicine, which was as certain to 
make its annual appearance as the spring house- 
cleaning. 
The A. racemosa grows here but sparingly, and 
A. hispida, I think, not at all. The family is 
pretty well represented, however, as, indeed, are 
many of the most interesting of our native plants, 
the moist soil of our sunny valley furnishing 
favorable conditions for growth. 
Moosup Valley, R. I. 
[Scientific American.] 
EDISON'S EXPLANATIOX OF THE AMPERE 
AND THE VOLT. 
During a recent examination « lawyer put the 
following question to Thomas A. Edison : 
" Explain what is meant by the number of volts 
in an electric current?" To which he replied : 
"I will have to use the analogy of a waterfall to 
exijlain. Say we have a current of water and a 
turbine wheel. If I have a turbine wheel and 
allow a thousand gallons per second to fall from a 
height of one foot on the turbine, I get a certain 
power, we will say one horse power. Xow the 
one foot of fall will represent one volt of pressure 
in electricity, and the thousand gallons will repre- 
sent the ampere or the amount of current. We 
will call that one ampere. Tims we have a thou- 
sand gallons of water, or one ampere, falling one 
foot, or one volt, or under one volt of pressure, 
and the water working the turbine gives one horse 
power. If, now, we go a thousand feet high, and 
take one gallon of water and let it fall on the tur- 
bine wheel, we will get the same power as we had 
before, namely, one horse power. We have got a 
thousand times less current or less water, and we 
will have a thousandth of an ampere in place of 
one ampere, and we will have a thousand volts in 
place of one volt, and we will have a fall of water 
a thousand feet as against one foot. Now the fall 
of water or the height from which it falls is the 
pressure or volts in electricity, and the amount of 
water is the amperes. It will be seen that a thou- 
sand gallons a minute falling on a man from a 
height of only one foot would be no danger to the 
man, and that if we took one gallon and took it 
up a thousand feet and let it fall down it would 
crush him. So it is not the quantity or current of 
water that does the damage, but it is the velocity 
or the pressure that produces the effect." 
[Science.] 
A XEW METHOD OF PREPARING OXYGEN 
GAS. 
Mr. Werner Langguth, writing to The En- 
gineering and Mining Journal, states that it may 
be of interest to some to learn of a comparatively 
cheap and practical method which will furnish an 
ample supply of pure oxygen gas from a solution 
of chloride of lime (blcaching-powder). The pro- 
duction of this gas and its method were observed 
and investigated by Mr. Langguth some years 
ago, and it has since Ijeen practically used by him 
in the laboratory for various purposes. If this 
method becomes generally known, it may find 
manifold application ow ing to its cheapness and 
simplicity. If a few- drops of a cobalt salt (nitrate 
of cobalt, Co(N03)2, for instance) be added to a 
strong solution of bleaching-powder in water, 
H,0 -I- CaCl^ -I- Ca(ClO),, and shaken well, an 
evolution of gas will be immediately ol)served, the 
production of which will be increased by a slight 
rise of temperature. The gas thus produced is 
pure oxygen, free from chlorine, and may be 
dried, if required, in the usual manner. The evo- 
lution is not violent, and the reaction gives an 
even and continuous flow of oxygen gas for a 
long time ; that is, until all the bleacliing-powder 
in solution is converted into calcium chloride : 
CaClj -I- Ca(ClO), -f- H,0 = 20 -|- 2CaClj -f- ILO. 
The few drops of nitrate of cobalt added are pre- 
cipitated by the bleaching-powder to cobalt 
hydroxide, which suffers no further change, only 
producing by its presence the liberation of the 
oxygcff. It is a beautiful illustration of its cata- 
lytic action. It is needless to say that the precip- 
itated oxides can be used over again, ad infinitum, 
with the same eftect. The calcium-chloride solu- 
tion is decanted from the settled cobalt hydroxide 
in the generator, charged with a fresh solution of 
bleaching-powder, shaken, and the evolution of 
oxygen commences again. Nickel salts will act 
on bleaching-powder in the same manner, but the 
evolution of oxygen is much slower. 
INDUSTRIAL MEMORANDA. 
Submarine Boat. — Hie French submarine boat 
"Gymnote" was recently tried at Toulon, and 
demonstrated its ability to pass through a block- 
aded line and escape attention in spite of syste- 
matic efforts to watch, trace, or discover its course. 
According to the Bevue Indnstrielle, it plunged and 
remained under water forty minutes. It rose to 
the surface at a distance of more than two miles 
and a half from its i)oint of departure, and had 
passed under the watched line of demarcation 
without being seen. After having ascertained 
where it was, it remerged to return. It again 
crossed the line, but this time two of the parties 
on the lookout for it got a glimpse of it, not, how- 
ever, sufficiently distinct to enable them to trace 
and pursue it. The course of the boat was in both 
instances rectilinear. 
Preserving Hemp Ropes. — In order to insure 
greater strength in ropes used for scaffolding pur- 
poses, particularly in localities where the atmos- 
phere is destructive of hemp fiber, such ropes 
should be dipped, when drj', into a bath contain- 
ing 20 grains of sulphate of copper per liter of 
water, and kept in this solution some four daj's, 
afterward being dried ; the ropers will thus have 
absorbed a certain quantity of sulphate of copper, 
which will preserve them for some time both from 
the attacks of animal parasites and from rot. The 
copper salt may be fixed in the fibers by a coating 
of tar or by soapy water, and in order to do this the 
rope is passed through a l»ath of boiled tar, hot, 
drawing it through a thiml)le to press back the ex- 
cess of tar, and suspending it afterward on a stag- 
ing to dry and harden. In a second method the 
rope is dijiped in a solution of 100 grammes of 
soap per liter of water. 
The casting talde in a plate-glass factory is 
about twenty feet long, fifteen feet wide, and 
seven inches thick. Strips of iron on each side of 
the table afford a bearing for the rollers, and de- 
termine the thickness of the plate of glass to be 
cast. The rough plate is commonly 9-16 inch, but 
after polishing it is reduced to 6-16 or 7-16., The 
casting tables are moimted on wheels and run on 
a track that reaches every furnace and annealing 
oven in the building. The molten glass having 
been poured on the table, the heavy iron roller 
passes from end to end, spreading the glass to a 
uniform thickness. In contact with the cold 
metal of the table the glass cools rapidly. Then 
the door of the annealing oven is opened and the 
plate of glass introduced. The floor of the oven 
is on the same level as the casting table, so that 
the transfer can be made quickly. When, after 
several days, the glass is taken out of the oven its 
surface is very rough and uneven. It is used in 
this condition for skylights and other purposes 
where strength is desired rather than transpar- 
ency. The greater part of the glass, however, is 
ground, smoothed, and polished. 
