Vol. XXIV. No. 9.] 
POPULAR SCIENCE NEWS. 
133 
II 
is used in large quantities in the manufacture 
of red fire. A small quantity of a salt of this 
metal, when volatilized in a flame, imparts a 
magnificent crimson color to it which can be 
obtained by no other substance. The nitrate 
of strontia is the salt most commonly used for 
this purpose. It is a curious fact that the 
spectroscope shows that the light from incan- 
descent strontium also_ contains a large pro- 
portion of blue rays, which are, however, 
masked b)' the much greater brilliancy of the 
red ones. 
Magnesium, formerly very rare, has recently 
become a comparatively common metal. It 
burns in the air with an extremely brilliant 
light, which is very rich in actinic, or chemi- 
cal rays. This property renders it useful 
in photography, and fine pictures can now 
be obtained at night or in dark rooms by the 
"Hash" of a few grains of the powdered 
metal blown through a flame. 
Cadmium is a metal resembling zinc, and 
usually occurring in the same ores. It has a 
limited but important use in the arts as a 
constituent of the fusible metal usAl for mak- 
ing low-water plugs in boilers, and automatic 
sprinklers for factories, where the metal melts 
and allows a water-valve to open when the 
temperature reaches a certain point. An 
alloy composed of three parts of cadmium, 
four of tin, fifteen of bismuth, and eight 
of lead, melts at about 160° F. — much below 
the boiling-point of water. Sulphide of cad- 
mium is of a brilliant yellow color, and is 
used by artists as a pigment. 
Cerium is a rare metal of the aluminium 
group, which is of value only from its sup- 
posed medicinal properties, being considered 
by some physicians to be of great value in 
certain forms of nausea. 
Vanadium is now used in considerable 
quantities in dyeing and cloth-printing works, 
on account of the remarkable oxidizing prop- 
erties of some of its compounds. It not only 
changes chloride of aniline into aniline black, 
but retains the power to an unlimitetl extent, 
so that a small quantity of vanadium salt will 
produce an indefinite quantity of aniline 
black. It seems to be alternately reduced 
and oxidized, thus acting as a carrier of oxy- 
gen to the aniline, but its peculiar action is 
not well understood. A few drops of vana- 
date of ammonia added to a decoction of galls 
forms a very fair black ink, which, however, 
soon fades into a permanent brown color. It 
is a quite uncommon metal, and the principal 
source of supply is from the slag of the 
Creusot steel works in France, which con- 
tains two per cent, of vanadic acid. 
• The salts of a metal called tungsten are 
used to render light cloths uninflammable. 
A very superior quality of steel is also ob- 
tained by alloying it with a small quantity 
of the metal. The "Mushet" steel is pre 
pared in this way. 
Iridium is usually associated with platinum, 
and is even more infusible and insoluble, 
besides being very much harder. By com- 
bining it with a small amount of phosphorus 
it becomes more fusible, without losing much 
of its hardness. The so-called "diamond" 
points of gold pens and stylographs are made 
of this metal, and it has now replaced agate 
for the knife-edges of chemical balances, 
and in other scientific apparatus. 
Zirconium, or rather its oxide zirconia, has 
recently found an extensive application in the 
manufacture of the "hoods" for the Wels- 
bach incandescent gas lights. This oxide, 
when heated in a gas flame, glows with a 
pure, steady, white light, equal to that of the 
incandescent electric lights, and costing much 
less. 
Selenium is not a metal, but belongs to 
the sulphur group of elements. We must 
mention, however, the wonderful property by 
which its electrical conductivity varies accord- 
ing to the amount of light falling upon it, 
just as the chemical relations of silver are 
altered by the same means. By this power 
Professor Bell was enabled to construct an 
optical telephone, and actually transmitted 
words and sentences between two distant 
points which were not connected jn any 
way except by a beam of light, which faith- 
fully carried the vibrations of his voice to a 
selenium disk, by which they were trans- 
formed into electric energy and reproduced 
in an ordinary telephone. Whether we shall 
ever be able to see our friends at a distance, 
as we now talk with them, is exceedingly 
problematical ; but if we ever do so, it will 
doubtless be through this mysterious connec- 
tion between light, electricity, and the element 
selenium. 
[Original in Popular Science News.} 
TWO CARBON COMPOUNDS. 
BY GEORGE L. BURDITT. 
Besides the three allotropic forms in which 
carbon occurs, it is found in a number of important 
inorganic compounds, a few of which are quite 
common, and at the same time quite interesting. 
One of the commonest of these compounds is car- 
bonicdioxide (CO2), sometimes called carbonicanhy- 
dride, or carbonic acid gas. This is formed when 
carbon is burned in air; but the best way of obtain- 
ing it for laboratory use is by the action of a strong 
acid upon calcic carbonate, the calcic carbonate 
being in the form of pure chalk or marble. The 
process is carried on in a retort or gas-flask, and the 
following reaction takes place, if hydrochloric acid 
is used : 
CaC03+2HCl=CaClj-l- HjC03=CaCl2 + H2O + CO2. 
The CO2 may be collected over water, or by dis- 
placement of air in the receiving vessel, it being 
heavier than air. 
Under ordinary conditions, COj is a colorless 
gas, having a slight acid taste and odor, and is 
heavier than air. It will neither burn nor support 
combustion. This may be illustrated by a simple 
experiment. CO2 is generated, and a tumbler is 
put into it in the same way it would be into water. 
When taken out again the tumbler is apparently 
empty, but is really full of the gas. The CO2 is then 
poured upon a lighted candle, in the same way as 
water would be, and the flame goes out. But CO2 is 
not the only gas that acts in this way, and so a 
special test is necessary. When lime-water is 
shaken with CO2 a white precipitate is formed, and 
in this way its presence may be detected. Besides 
being heavier than air, CO2 does not diffuse very 
readily, and has a tendency to sink, often settling in 
old cellars, mines, vats, etc. It does not support 
life any more than it does combustion, and men 
going down into cellars or mines in which it has 
settled are frequently overcome and die before help 
can reach them. Therefore, it is always wise to 
lower a lighted candle into such a place before 
descending. If the candle burns, the air can be 
breathed with safety ; if not, the air is dangerous. 
Carbonic dioxide is deadly because it acts as a 
poison when breathed into the lungs, acting directly 
upon the blood. Striking examples of this may be 
seen at the Grotto del Cane, a small grotto in 
Southern Italy, partly filled with CO2 gas. A man 
may stand upright in this grotto and not be affected, 
because the gas extends no higher than his shoulder; 
but a dog, when thrown in, is almost instantly 
killed. Another example is the Vale of Death, 
near Batar, Java, — a sort of valley filled with CO2. 
Upon looking into it, the spectator sees the ground 
strewn with the bones of animals and birds which 
have unconsciously entered and been overcome. 
CO2 is a difficult gas to condense. It is soluble in 
about its own bulk of water, but more is absorbed 
under pressure. The gas escapes with rapid effer- 
vescence when the pressure is removed. Water 
thus charged is known as soda water, and the excess 
of gas forced into the water gives the agreeable 
taste. And here it maybe noted that carbonic acid, 
although poisonous when breathed into the lungs, 
is harmless — and sometimes even beneficial — when 
taken into the stomach. A solution of CO2 in 
water — HaCOs in the above reaction — gives a weak 
acid reaction ; but the acid is very unstable, and 
breaks up into water and carbonic acid gas, as 
shown by the reactions. Although a weak acid, it 
forms an important class of salts, called carbonates. 
All carbonates dissolve in dilute nitric acid, with 
brisk effervescence, and those of the alkaline metals 
are soluble in water. 
Besides the sources already described, carbonic 
dioxide is formed in great quantities in nature. 
1. Great quantities are formed by the respiration 
of men and animals, the proportion in respired air 
being from three to four per cent. This free CO2 
does not injure anyone, because there is so little 
of it, and because the air, which is always in motion, 
diffuses it. Plants absorb the C to form their 
tissues, and give oft" the O2, which is necessary to 
sustain animal life. 
2. CO2 is also formed in the fermentation 
of beer, champagne, and some other liquors, and 
causes their sharp taste. It is formed in the process 
of bread-making from yeast or baking-powder, and 
rises through the dough in bubbles, causing the 
bread to rise. 
3. In burning lime in the lime-kiln, the heat 
drives off great quantities of carbonic oxide from 
the limestone, and it escapes. This process goes 
on under ground as well as above. In certain 
volcanic regions subterranean heat acts upon lime- 
stone, setting free large volumes of this gas, which 
finds its way into the atmosphere through the craters 
of volcanos or fissures in the earth. The springs 
in such places are sometimes strongly charged with 
it, the gas escaping with effervescence when the 
springs reach the surface. 
