Vol. XXIV. No. S.] 
POPULAR SCIENCE NEWS. 
117 
[Original in Popular Science News.} 
OUR COMMON PIGMENTS. 
BY LYMAN G. SMITH. 
Nearly all our cominon colors are either chemi- 
cal preparations or natural mineral earths. 
Of the bl.ick pigments, lampblack is the cheapest 
and most common. It consists of nearly pure car- 
bon, deposited in the familiar form called soot. It 
is manufactured by burning .some hjdro-carbon with 
an insufficient supply of air. Pine knots and resin are 
frequently employed for the purpose. The dense 
smoke which results from the imperfect combustion 
is drawn through a chamber lined with canvas or 
sheepskin, and having an outlet in the roof. As the 
lamp-black accumulates on the walls it is scraped 
down to the floor from time to time by lowering a 
dome from the roof. This dome has the shape of 
an inverted funnel, and is made to fit inside of the 
chamber. This pigment is very stable, as it consists 
essentially of carbon and is unaltered by all ordinary 
conditions. A lamp-black called "gas-black" is 
sometimes made from coal gas. 
Another black pigment is the so-called ivory- 
black. This is made 
either from the bone- 
charcoal, formed by 
heating bones to red- 
ness in closed vessels, 
or from the soot pro- 
duced by the imperfect 
combustion of an oil 
formed by the distilla- 
tion of bones. In the 
latter case it must 
necessarily be the 
same as lamp-black. 
When made from 
bone-charcoal, how- 
ever, it contains sev- 
eral of the mineral 
constituents of the 
bones, which give it 
a different character. 
It is necessary to sub- 
ject the bone-charcoal 
to a most thorough 
grinding, and the last 
time it is ground, oil 
is generally used, and 
it is placed upon the 
market in this form. 
A very fine quality of 
ivory-black is said to 
be made from the genuine ivory. 
Among the white paints, white lead certainly 
stands at the head. It is a basic plumbic carbonate. 
The ordinary method of manufacture is as follows : 
The metallic lead, in sheet form, coiled up, or cast 
into buckles, is placed in earthen pots. These pots 
have a few inches of vinegar or acetic acid in the 
bottom. The pots are covered, and piled up in 
sheds, buried in spent tan or manure. The heat de- 
veloped by the decay of the organic matter volatilizes 
a little of the acetic acid, changing the lead into a 
basic acetate. The basic acetate is in turn changed 
into the basic carbonate by the carbonic dioxide 
given off by the decaying of the organic matter. 
The process takes from four to six weeks. The white 
lead is carefully removed and ground in oil. It has 
a wonderful covering power, and combines remark- 
ably well with oil, two properties which the substi- 
tutes which have been proposed lack. On the other 
hand, it blackens very rapidly when exposed to sul- 
phureted hydrogen, and is very poisonous to those 
engaged in its manufacture. 
Zinc-white, which has been used to some extent 
as a substitute for white lead, is an oxide of zinc. It 
is made by heating the native red oxide in a current 
of air. The zinc-white is formed as a flocculent 
mass, which is blown through passages to purify it, 
and is finally collected in tiannel bags. It is gener- 
ally sold ground in oil like white lead. 
Another white pigment is occasionally used, called 
permanent white. The name is very inappropriate, 
as it does not readily combine with the oil, and rubs 
otT easily. It is used to adulterate the other white 
paints. It is sulphate of baryta, BaSOj, prepared in 
the wet way by precipitation, which is the better 
method, or by grinding the natural baric sulphate, 
known as heavy spar. 
Prussian-blue is probably the most important blue 
pigment. It is a chemical product, obtained by pre- 
cipitation. It is principally a compound of cvano- 
gen and iron, Fe4(Fe[CN](i).-!. It was accidentally 
discovered by Diesbach, a color-maker of Berlin, 
early in the iSth century. It is obtained by adding 
an excess of a ferric salt to potassic ferrocy-inide. 
In practice a ferrous salt is generally used, and the 
precipitate afterwards subjected to oxidizing agents. 
It is carefully purified, washed, and dried, and is put 
ANCIENT CHEMICAL LAIiOltATOIlY. (See p;ige ii6.) 
upon the market either ground in oil or dried. 
Ultramarine has a very interesting history. It 
was formerly obtained from the rare mineral, lapis 
lazuli, in which it occurred native. The process 
of obtaining it was a very difficult and tedious one. 
The credit of the discovery of an artificial method 
of preparation is generally conceded to Guimet, a 
French chemist. He was led to the discovery by 
noticing a certain product in his furnaces, which, 
on examipation, proved to be identical with the nat- 
ural ultramarine. The method of preparation, which, 
with only slight modifications, is the same now as 
then, was as follows: Aluminic hydrate was first 
made from alum free from iron, and this was mixed 
with soda ley saturated with precipitated silica. 
The mixture was then evaporated, and the residue 
mixed with flowers of sulphur. An equal portion 
of a mixture of dry sodic sulphate and flowers 
of sulphur was then weighed out, mixed with the 
first preparation, and the whole thoroughly mixed 
and rammed into a crucible, filling it completely ; 
the crucible was then suddenly heated to redness, 
and kept so for two hours. It was finally cooled 
with the cover on, and the resulting greenish yellow 
product was again heated in very porous crucibles. 
It was then levigated and washed, giving the pig- 
ment in the powdered state. The value of this 
discovery may readily be seen from the fact that the 
price is .said to have fallen in England from five guin- 
eas per ounce, to about a shilling per pound. It is a 
good stable color, and a very brilliant blue. 
Chrome yellow is a chemical product, plumbic 
chroniate, PbCrOj. The best quality is made by 
precipitation from plumbic acetate by potassic chro- 
niate or potassic dichromate. It is a very fine 
yellow, and an important pigment. 
Vermilion is the most brilliant red. It is formed 
either from the natural sulphide of mercury, cinna- 
bar, or from an artificial sulphide. Its brilliant 
color depends in great measure upon its being in a 
finely divided state. It is generally made artificially 
by subliming a mixture of sulphur and mercury, 
and pulverizing the artificial cinnabar formed by the 
process. It may also be made by a wet process. 
Chinese vermilion, which is said to be m.ide by 
a laborious mechani- 
cal process, is the 
purest and best. Ver- 
milion is a very bril- 
liant pigment, but is 
apt to grow dark when 
exposed. 
The ochres form a 
large class of useful 
colors. They consist 
principally of a clay, 
colored by certain ox- 
ides of iron. They 
contain water, and are 
gently heated to expel 
it, when they are 
known as "raw" col- 
ors. If calcined they 
turn reddish and are 
said to be "burnt." 
Umber and sienna 
take their names from 
the places where they 
were formerly ob- 
tained in Italy. They 
are much used in 
stains. Some of the 
roof paints contain 
much hematite, and 
have a very good red 
color. Owing to their cheapness and perma- 
manence, the earth colors are very much used. 
They furnish a great variety of yellow and brownish 
reds. 
«♦► 
DIFFERENT KINDS OF LIGHTNING. 
1. As to the term " forked lightning," the repre- 
sentations of it given by artists, which resemble the 
so-called thunderbolts placed in the hand of Jupiter, 
are quite absurd. The flash, when photographed, 
exhibits itself as a line which is continually chang- 
ing its course, and is described as "intensely 
crooked" by a very careful observer. It never 
proceeds for a time in a straight line, and then, 
turning at a sharp angle, going on further in an 
equally straight line, as is represented in pictures. 
The forking of it is very marked, and this occurs by 
side flashes passing oft' from the main track, and 
eventually losing themselves, like the ramifications 
of tree roots. Occasionally the lightning appears 
to starf from a point from which several flashes 
diverge in different directions. 
2. " Sheet Lightning." — Whenever a flash passes 
from cloud to earth, the light produced by it illumi- 
