Vol. XXIV. No. 12.] 
POPULAE SCIENCE NEWS. 
181 
state, in both crystalline and arborescent 
forms. It also occurs amalgamated with 
mercury, and as chloride and sulphide. In 
most cases, however, the silver occurs as a 
sidphide, in connection with much larger 
proportions of the sulphides of lead, anti- 
monv, or iron. Galena, or sulphide of 
lead, a very common mineral, usually con- 
tains varying proportions of silver, and the 
ores of copper often contain enough of the 
more precious metal to pay for its separation. 
The extraction of silver from its ores requires 
long and rather complicated processes ; but, 
on a large scale, it can be accomplished very 
cheaply, and a comparatively poor ore will 
pay for its working. There are many old 
mines in Mexico and the West of which the 
refuse left by the ancient miners can be 
worked over at a profit. 
Unlike gold, which always occurs in the 
metallic state, the ores of silver are not 
readily recognized or worked by savage or 
semi-civilized peoples, and it has occasionally 
happened that among such peoples silver has 
been valued higher than gold ; but the usual 
ratio between the price of silver and gold 
of about I to 20 has obtained more or less 
constantly for many years. 
Silver is the best conductor of heat and 
electricity known, slightly exceeding copper 
this respect. The physical and chemical 
elations between these two metals are very 
tlose in many other wavs, and if the "trans- 
lutatiori of the elements " is ever accom- 
blished, — a very unlikely matter, by the way, 
t — we may expect that these two metals will 
'he shown to be at least brothers in the chemi- 
cal family. 
The easy reduction of salts of silver to the 
metallic state renders it particularly adapted 
for electro-plating. Formerly the plating 
of cheaper metals by silver was accomplished 
by amalgamation with mercury, or other 
chemical means, but these processes have 
been almost entirely superseded by the use 
of the electric current, which rapidly decom- 
, poses a solution of cyanide of silver, and 
deposits a bright and perfect coating of the 
metal upon articles immersed in it. 
Silvering upon glass is eflected by means 
; 'of certain organic substances which have the 
power of precipitating silver from its solu- 
tions. When a solution of oxide of silver in 
immonia is gently heated with Rochelle 
jlts, glucose, glycerine, or tartaric acid, in a 
blean glass or porcelain vessel, a bright coat- 
ing of metallic silver is deposited upon the 
tides. Glass door-knobs, small mirrors, lan- 
ern reflectors, and the ornamental glass 
►lobes sometimes placed in gardens or parks, 
Jre silvered in this way, as well as the mir- 
i"ors used in certain reflecting telescopes. 
Although silver has but little affinity for 
jxygen, it unites with the allied element, sul- 
Iphur, more readily than any other metal. 
The ''tarnish" which articles of silver take 
on when exposed to the air is due to the 
formation of a thin film of sulphide, from 
the traces of sulphur compounds usually 
present in the air. The discoloration of a 
silver spoon with which an egg has been 
eaten is a familiar example, and has led to 
the manufacture by enterprising jewellers 
of platinum egg-spoons, which are unaffected 
by the sulphur compounds present in this 
popular breakfast dish. Everyone who has 
carried matches and silver coins in the same 
pocket must also have noticed this undesirable 
combination. 
The most remarkable chemical property 
of silver, however, is found in its relation to 
light. It does not stand alone in this respect, 
for compounds of iron, chromium, and many 
other substances have their composition modi- 
fied by this mysterious form of energy of the 
light beam ; but silver is pre-eminent in this 
respect, and the wonderful change which 
is caused by this means in a film of chloride, 
bromide, or iodide of silver is the basis of the 
most beautiful modern art of photography. 
Many years ago it was noticed that chloride 
of silver blackened when exposed to the 
sun's rays, and from this simple observation 
the labors of Daguerre, Niepce, Draper, and 
their many successors have led to the present 
remarkable development of an art which 
produces pictures, superior to the works of 
the best artists, at a nominal price, and by a 
process so simple that it is successfully prac- 
ticed by thousands of amateurs, with no 
especial scientific knowledge, as a recreation 
and amusement. 
This action of light upon certain salts of 
silver is especially remarkable as showing the 
connection between matter and energy, or, 
more strictly, between those forms of energy 
known as chemical affinity and actinism. 
The molecules of bromide of silver in the 
sensitive film are held together by some 
attractive force which we know little about, 
but call chemical affinity. Something — some 
force, or energy — comes to us in the sunbeam 
which enters into these molecules aid forces 
them apart, into other combinations ; but 
just what it is or how it is accomplished is 
something which we cannot explain In the 
case of the element selenium, its Blectrical 
relations are similarly modified by the dis- 
turbing influence of the solar radian; energy, 
thus showing an intimate connection between 
them ; and, although it has long been known 
that light, heat, power, actinism, electricity, 
and chemical affinity were but different mani- 
festations of a single form of energy, the 
results of modern investigations tend to show 
that the connection between them is much 
closer than has ever been suspected, and that 
we are, perhaps, on the eve of discoveries in 
regard to the nature and properties of matter 
and enerirv which will revolutionize the theo- 
ries formulated from the facts at present 
known to us. 
INDUSTRIAL MEMORANDA. 
Professor Scheibler lias invented a machine 
for producing artificial smoke on a battlefield, wfiich, 
it is believed, will be of great value to counteract 
on some occasions tfie introduction of smokeless 
powder. 
A New Application of the Telephone for 
military purposes is sliortly to be introduced into 
the Italian fortress artillery. It consists of a so- 
called telephonic bonnet, to be worn by each officer 
when in charge of a gun, which will enable him to 
receive the instructions of the commander-in-chief 
or other in the quickest possible time. 
Rubber Pavements. — A portion of the Boulevard 
Anspach, Brussels, is being laid with a new paving 
called "caoutchouc macadam." It is a mixture 
of india-rubber and certain stones ground together 
and converted into a soft paste by heat. The new- 
material is not slippery, and is said to withstand the 
heat of summer or the cold of winter, while being 
very durable. 
Cement for Pestle Handles. — A good cement 
for fastening porcelain or wedgewood pestles to 
wooden handles consists of a stiff paste made by 
the addition of glycerine to litharge. This should 
be applied to the wooden handle, and care taken 
that a close joint be made at the point of union, so 
that all danger of contaminating substances in the 
mortar may be avoided. 
Waterproofing Cloth. — Hime and Noad use 
for waterproofing textile fabrics a solution of cotton, 
or other vegetable fibre, in an ammoniacal copper 
solution containing four parts of copper. From 
this solution the copper is precipitated with zinc, 
when a colorless, viscid solution of ammonium 
zincate and vegetable matter is obtained, in which 
the tissue is immersed to impregnation, pressed, 
dried, and wet-calendered. 
Case Hardening by Electricity. — Professor 
Elihu Thomson has recently devised a method 
of case hardening iron or steel by means of the 
heat produced by the passage of an electric current. 
His process consists essentially in heating the object 
electrically, and then applying to the metal so 
heated a surrounding envelope — either gaseous, 
fluid, or solid — for the purpose of changing or pre- 
venting change in the quality of the material, 
according to the special end to be attained. 
Firing Boilers — One of the highest aims of an 
expert fireman should be to keep the largest possible 
portion of his grate area in a condition to give great 
radiant heat the largest possible part of a day ; when 
using anthracite coal, by firing light, quick, and often, 
not covering all of the incandescent coals ; when 
using bituminous coal, by coking it very near the dead 
plate, allowing some air to go through openings in the 
door, and by pushing toward the bridge wall only 
live coals; when slicing, to open the door only 
far enough to work the bar. 
A Big Blast was exploded at the Dinorwic 
Quarries, Carnarvonshire, lately, by which about a 
quarter of a million of tons of rock were removed. 
The part to be removed was an obstructive rock 
which prevented the quarrymen from carrying on 
their work. About 7 000 pounds of gelatine, equal 
in strength to twenty tons of gunpowder, was used 
in the blast, which was the greatest ever attempted 
in North Wales, the cost of the explosive being 
about $3,000, and the quantity of rock displaced 
being so enormous that it will take some hundreds 
of men nine months to remove it. 
