about nine notches running around it in distances of about 5/8 of an
inch. Next, the foremost notched piece is heated in a forge in such a
manner that the remaining portion of the bar is heated less by the fire
proper than by the transmitted heat. When the foremost piece is heated
to burning, i. e., to combustion, and the color of the succeeding
pieces gradually passes to dark-brownish redness, the whole rod is
hardened. A test with the file will now show that the foremost burned
piece possesses the greatest hardness, that several softer pieces will
follow, and that again a piece ordinarily situated in the second third,
whose temperature was the right one for hardening, is almost as hard as
the first one. If the different pieces are knocked off, the fracture
of the piece hardened at the correct temperature exhibits the finest
grain. This will give one an idea of the temperature to be employed for
hardening the steel in question and its behavior in general. Very hard
steel will readily crack in this process.
«Welding Compound.»—Boracic acid, 41 1/2 parts; common salt 35 parts;
ferrocyanide of potassium, 20 parts; rosin, 7 1/2 parts; carbonate of
sodium, 4 parts. Heat the pieces to be welded to a light-red heat and
apply the compound; then heat to a strong yellow heat and the welding
may be accomplished in the usual manner.
The precaution should be observed, the same as with any of the
cyanides, to avoid breathing the poisonous fumes.
«Softening Steel.»—Heat the steel to a brown red and plunge into soft
water, river water being the best. Care should be taken, however, not
to heat over brown red, otherwise it will be hard when immersed. The
steel will be soft enough to be cut with ease if it is plunged in the
water as soon as it turns red.
«Draw-Tempering Cast Steel.»—First heat the steel lightly by means of
charcoal until of a cherry-red shade, whereupon it is withdrawn to be
put quickly into ashes or dry charcoal dust until completely cooled.
The steel may also be heated in the forge to a red cherry color, then
hammered until it turns blue and then plunged into water.
«Drilling Hard Steel.»—To accomplish the object quickly, a drill of
cast steel should be made, the point gradually heated to the red, the
scales taken off, and the extremity of the point immersed at once in
quicksilver; then the whole quenched in cold water. Thus prepared,
the drill is equal to any emergency; it will bore through the hardest
pieces. The quantity of quicksilver needed is trifling.
«Engraving or Etching on Steel.»—Dissolve in 150 parts of vinegar,
sulphate of copper, 30 parts; alum, 8 parts; kitchen salt, 11 parts.
Add a few drops of nitric acid. According to whether this liquid is
allowed to act a longer or shorter time, the steel may be engraved
upon deeply or the surface may be given a very ornamental, frosted
appearance.
«To Distinguish Steel from Iron.»—Take a very clean file and file over
the flame of an alcohol lamp. If the filed piece is made of steel,
little burning and crackling sparks will be seen. If it consists of
iron, the sparks will not crackle.
STEEL, BROWNING OF: See Plating.
STEEL, DISTINGUISHING IRON FROM: See Iron.
STEEL ETCHING: See Etching.
STEEL-HARDENING POWDER: See Iron.
STEEL, OXIDIZED: See Plating.
STEEL PLATING: See Plating.
STEEL POLISHES: See Polishes.
STEEL, TO CLEAN: See Cleaning Preparations and Methods. {688}
STENCILS FOR PLOTTING LETTERS OF SIGN PLATES: See Enameling.
STENCIL INKS: See Inks.
«STEREOCHROMY.»
Stereochromatic colors can be bought ground in a thickly liquid
water-glass solution. They are only diluted with water-glass solution
before application on the walls. The two solutions are generally
slightly dissimilar in their composition, the former containing less
silicic acid, but more alkali, than the latter, which is necessary
for the better preservation of the paint. Suitable pigments are zinc
white, ocher with its different shades of light yellow, red, and dark
brown, black consisting of a mixture of manganese and lampblack,
etc., etc. White lead cannot be used, as it coagulates with the water
glass, nor vermilion, because it fades greatly under the action of
the light. The plastering to be coated must be porous, not fresh, but
somewhat hardened. Otherwise the caustic lime of the plaster will
quickly decompose the water glass. This circumstance may account for
the unsatisfactory results which have frequently been obtained with
water-glass coatings. Before applying the paint the wall should first
be impregnated with a water-glass solution. The colors may be kept
on hand ground, but must be protected from contact with the air. If
air is admitted a partial separation of silica in the form of a jelly
takes place. Only pure potash water glass, or, at least, such as only
contains little soda, should be used, as soda will cause efflorescence.
STEREOPTICON SLIDES: See Photography.
STEREOTYPE METAL: See Alloys.
«STONE, ARTIFICIAL.»
The following is a process of manufacture in which the alkaline
silicates prepared industrially are employed.
The function of the alkaline silicates, or soluble glass, as
constituents of artificial stone, is to act as a cement, forming with
the alkaline earths, alumina, and oxide of lead, insoluble silicates,
which weld together the materials (quartz sand, pebbles, granite,
fluorspar, and the waste of clay bricks). The mass may be colored black
by the addition of a quantity of charcoal or graphite to the extent of
10 per cent at the maximum, binoxide of manganese, or ocher; red, by
6 per cent of colcothar; brick red, by 4 to 7 per cent of cinnabar;
orange, by 6 to 8 per cent of red lead; yellow, by 6 per cent of yellow
ocher, or 5 per cent of chrome yellow; green, by 8 per cent of chrome
green; blue, by 6 to 10 per cent of Neuwied blue, Bremen blue, Cassel
blue, or Napoleon blue; and white, by 20 per cent, at the maximum, of
zinc white.
Chrome green and zinc oxide produce an imitation of malachite. An
imitation of lapis lazuli is obtained by the simultaneous employment
of Cassel blue and pyrites in grains. The metallic oxides yield the
corresponding silicates, and zinc oxide, mixed with cleansed chalk,
yields a brilliant marble. The ingredients are mixed in a kind of
mechanical kneading trough, furnished with stirrers, in variable
proportions, according to the percentage of the solution of alkaline
silicate. The whole is afterwards molded or compressed by the ordinary
processes.
The imitation of granite is obtained by mixing lime, 100 parts; sodium
silicate (42° Bé.), 35 parts; fine quartz sand, 120 to 180 parts; and
coarse sand, 180 to 250 parts.
Artificial basalt may be prepared by adding potassium sulphite and lead
acetate, or equal parts of antimony ore and iron filings.
To obtain artificial marble, 100 pounds of marble dust or levigated
chalk are mixed with 20 parts of ground glass and 8 parts of fine
lime and sodium silicate. The coloring matter is mixed in proportion
depending on the effect to be produced.
A fine product for molding is obtained by mixing alkaline silicate, 100
parts; washed chalk, 100 parts; slaked lime, 40 parts; quick lime, 40
parts, fine quartz sand, 200 parts; pounded glass, 80 parts; infusorial
earths, 80 parts; fluorspar, 150 parts. On hardening, there is much
contraction.
Other kinds of artificial stone are prepared by mixing hydraulic lime
or cement, 50 parts; sand, 200 parts; sodium silicate, in dry powder,
50 parts; the whole is moistened with 10 per cent of water and molded.
A hydraulic cement may be employed, to which an alkaline silicate is
added. The stone or object molded ought to be covered with a layer of
fluosilicate. {689}
A weather-proof water-resisting stone is manufactured from sea mud, to
which 5 per cent of calcic hydrate is added. The mass is then dried,
lixiviated, and dried once more at 212° F., whereupon the stones are
burned. By an admixture of crystallized iron sulphate the firmness of
these stones is still increased.
«Sand-Lime Brick.»—In a French patent for making bricks from pitch and
coal tar, powdered coke and sea sand are gently heated in a suitable
vessel, and 20 per cent of pitch and 10 per cent of coal tar added,
with stirring. The pasty mass obtained is then molded under pressure.
The product obtained may be employed alone, or together with a
framework of iron, or with hydraulic lime or cement.
According to a French patent for veining marble, etc., in one or more
colors, coloring matters of all kinds are mixed with a sticky liquid,
which is then spread in a very thin layer on the surface of another
immiscible and heavier liquid. By agitating the surface, colored
veins, etc., are obtained, which are then transferred to the object
to be decorated (which may be of most varied kind) by applying it to
the surface of the heavy liquid. A suitable composition with which
the colors may be mixed consists of: Oil of turpentine, 100 parts;
colophony, 10 parts; linseed oil, 10 parts; _siccatif soleil_, 5 parts.
The heavy liquid may be water, mercury, etc.; and any colors, organic
or mineral, may be used.
«CONCRETE.»
Concrete is the name applied to an artificial combination of various
mineral substances which under chemical action become incorporated
into a solid mass. There are one or two compositions of comparatively
trifling importance which receive the same name, though differing
fundamentally from true concrete, their solidification being
independent of chemical influence. These compositions only call for
passing mention; they are: _Tar concrete_, made of broken stones
(macadam) and tar; _iron concrete_, composed of iron turnings, asphalt,
bitumen, and pitch; and _lead concrete_, consisting of broken bricks
set in molten lead. The last two varieties, with rare exceptions,
are only used in connection with military engineering, such as for
fortifications.
Concrete proper consists essentially of two groups or classes of
ingredients. The first, termed the _aggregate_, is a heterogeneous
mass, in itself inactive, of mineral material, such as shingle, broken
stone, broken brick, gravel, and sand. These are the substances most
commonly in evidence, but other ingredients are also occasionally
employed, such as slag from iron furnaces. Burnt clay, in any form,
and earthenware, make admirable material for incorporation. The second
class constitutes the active agency which produces adhesion and
solidification. It is termed the matrix, and consists of hydraulic lime
or cement, combined with water.
One of the essential features in good concrete is cleanliness and an
entire absence of dirt, dust, greasy matter, and impurities of any
description. The material will preferably be sharp and angular, with
a rough, porous surface, to which the matrix will more readily adhere
than to smooth, vitreous substances. The specific gravity of the
aggregate will depend upon the purpose for which the concrete is to be
used. For beams and lintels, a light aggregate, such as coke breeze
from gasworks, is permissible, especially when the work is designed to
receive nails. On the other hand, for retaining walls, the heaviest
possible aggregate is desirable on the ground of stability.
The aggregate by no means should be uniform in size. Fragments of
different dimensions are most essential, so that the smaller material
may fill up the interstices of the larger. It is not infrequently
stipulated by engineers that no individual fragment shall be more than
4 inches across, and the material is often specified to pass through a
ring 1 1/2 to 2 inches in diameter. The absolute limits to size for
the aggregate, however, are determinable by a number of considerations,
not the least important of which is the magnitude and bulk of the work
in which it is to be employed. The particles of sand should also be of
varying degrees of coarseness. A fine, dust-like sand is objectionable;
its minute subdivision prevents complete contact with the cement on all
its faces. Another desideratum is that the particles should not be too
spherical, a condition brought about by continued attrition. Hence, pit
sand is better in many cases than river sand or shore sand.
The matrix is almost universally Portland cement. It should not be used
in too hot a condition, to which end it is usually spread over a wooden
floor to a depth of a few inches, for a few days prior to use. By
this means, the aluminate of lime becomes partially hydrated, and its
activity is thereby modified. {690} Roman cement and hydraulic lime may
also be used as matrices.
Portland cement will take a larger proportion of sand than either Roman
cement or hydraulic lime; but with the larger ratios of sand, its
tenacity is, of course, correspondingly reduced. One part of cement to
4 parts of sand should therefore be looked upon as the upper limit,
while for the strongest mortar the proportion need hardly exceed 1 part
of cement to 1 1/2 or 2 parts of sand. In the ensuing calculations
there is assumed a ratio of 1 to 3. For impermeability, the proportion
of 1 to 2 should be observed, and for Roman cement this proportion
should never be exceeded. The ratio will even advantageously be limited
to 2 to 3. For hydraulic lime equal parts of sand and cement are
suitable, though 2 parts of sand to 1 part of cement may be used.
The quantity of mortar required in reference to the aggregate is based
on the vacuities in the latter. For any particular aggregate the amount
of empty space may be determined by filling a tank of known volume
with the minerals and then adding sufficient water to bring to a level
surface. The volume of water added (provided, of course, the aggregate
be impervious or previously saturated) gives the net volume of mortar
required. To this it is necessary to make some addition (say 10 per
cent of the whole), in order to insure the thorough flushing of every
part of the work.
Assuming that the proportion of interstices is 30 per cent and adding
10 for the reason just stated, we derive 40 parts as the quantity of
mortar to 100 − 10 = 90 parts of the aggregate. An allowance of 1/4
volume for shrinkage brings the volume of the dry materials (sand and
cement) of the mortar to 40 + 40/3 = 53 1/3 parts, which, divided
in the ratio of 1 to 3, yields:
Cement (53 1/3)/4 = 13 1/3 parts
Sand, 3/4 x 53 1/3 = 40 parts
Aggregate 90 parts
───────
Total 143 1/3 parts
As the resultant concrete is 100 parts, the total shrinkage is 30 per
cent. Expressed in terms of the cement, the concrete would have a
composition of 1 part cement, 3 parts sand, 7 parts gravel and broken
stone, and it would form, approximately, what is commonly known as 7 to
1 concrete.
There are other ratios depending on the proportion of sand. Thus we
have:
Cement Sand Aggregate
1 1 1/2 4 1/3
1 2 5
1 2 1/2 6
1 3 7
1 3 1/2 7 1/2
1 4 8 1/4
The cost of concrete may be materially reduced without affecting
the strength or efficacy of the work, by a plentiful use of stone
“plums” or “burrs.” These are bedded in the fluid concrete during its
deposition _in situ_, but care must be taken to see that they are
thoroughly surrounded by mortar and not in contact with each other.
Furthermore, if they are of a porous nature, they should be well wetted
before use.
The mixing of concrete is important. If done by hand, the materials
forming the aggregate will be laid out on a platform and covered by the
cement in a thin layer. The whole should be turned over thrice in the
dry state, and as many times wet, before depositing, in order to bring
about thorough and complete amalgamation. Once mixed, the concrete is
to be deposited immediately and allowed to remain undisturbed until the
action of setting is finished. Deposition should be effected, wherever
possible, without tipping from a height of more than about 6 feet,
as in greater falls there is a likelihood of the heavier portions of
the aggregate separating from the lighter. In extensive undertakings,
concrete is more economically mixed by mechanical appliances.
The water used for mixing may be either salt or fresh, so far as the
strength of the concrete is concerned. For surface work above the
ground level, salinity in any of the ingredients is objectionable,
since it tends to produce efflorescence—an unsightly, floury deposit,
difficult to get rid of. The quantity of water required cannot be
stated with exactitude; it will depend upon the proportion of the
aggregate and its porosity. It is best determined by experiment in each
particular case. Without being profuse enough to “drown” the concrete,
it should be plentiful enough to act as an efficient intermediary
between every particle of the aggregate and every particle of the
matrix. Insufficient moisture is, in fact, as deleterious as an excess.
«Voids.»—The strength of concrete depends greatly upon its density, and
this is secured by using coarse material which contains the smallest
amount of voids or empty spaces. Different kinds of sand, {691}
gravel, and stone vary greatly in the amount of voids they contain,
and by judiciously mixing coarse and fine material the voids may be
much reduced and the density increased. The density and percentage of
voids in concrete material may be determined by filling a box of 1
cubic foot capacity and weighing it. One cubic foot of solid quartz or
limestone, entirely free from voids, would weigh 165 pounds, and the
amount by which a cubic foot of any loose material falls short of this
weight represents the proportion of voids contained in it. For example,
if a cubic foot of sand weighs 115 1/2 pounds, the voids would be
49 1/2-165ths of the total volume, or 30 per cent.
The following table gives the per cent of voids and weight per cubic
foot of some common concrete materials:
Per
Cent Wt. per
Voids Cu. Ft.
Sandusky Bay sand 32.3 111.7 pounds
Same through 20-mesh screen 38.5 101.5 pounds
Gravel, 1/8 to 1/4 inch 42.4 95.0 pounds
Broken limestone, egg-size 47.0 87.4 pounds
Limestone screenings, dust to 1/2 inch 26.0 122.2 pounds
It will be noted that screening the sand through a 20-mesh sieve, and
thus taking out the coarse grains, considerably increased the voids
and reduced the weight; thus decidedly injuring the sand for making
concrete.
The following figures show how weight can be increased and voids
reduced by mixing fine and coarse material:
Per
Cent Wt. per
Voids Cu. Ft.
Pebbles, about 1 inch 38.7 101.2 pounds
Sand, 30 to 40 mesh 35.9 105.8 pounds
Pebbles plus 38.7 per cent sand, by vol. 19.2 133.5 pounds
Experiments have shown that the strength of concrete increases greatly
with its density; in fact, a slight increase in weight per cubic foot
adds very decidedly to the strength.
The gain in strength obtained by adding coarse material to mixtures
of cement and sand is shown in the following table of results of
experiments made in Germany by R. Dykerhoff. The blocks tested were
2 1/2-inch cubes, 1 day in air and 27 days in water.
──────────────────────────+─────────+────────────
Proportions by Measure. │ Per │ Compression
│ Cent. │ Strength.
│ Cement. │
────────+───────+─────────+─────────+────────────
Cement. │ Sand. │ Gravel. │ By │ Lbs. per
│ │ │ Volume. │ Sq. In.
────────+───────+─────────+─────────+────────────
1 │ 2 │ — │ 33.0 │ 2,125
1 │ 2 │ 5 │ 12.5 │ 2,387
1 │ 3 │ — │ 25.0 │ 1,383
1 │ 3 │ 6 1/2 │ 9.5 │ 1,515
1 │ 4 │ — │ 20.0 │ 1,053
1 │ 4 │ 8 1/2 │ 7.4 │ 1,204
────────+───────+─────────+─────────+────────────
These figures show how greatly the strength is improved by adding
coarse material, even though the proportion of cement is thereby
reduced. A mixture of 1 to 12 1/2 of properly proportioned sand and
gravel is, in fact, stronger than 1 to 4, and nearly as strong as 1 to
3, of cement and sand only.
In selecting materials for concrete, those should be chosen which give
the greatest density. If it is practicable to mix two materials, as
sand and gravel, the proportion which gives the greatest density should
be determined by experiment, and rigidly adhered to in making concrete,
whatever proportion of cement it is decided to use. Well-proportioned
dry sand and gravel or sand and broken stone, well shaken down, should
weigh at least 125 pounds per cubic foot. Limestone screenings, owing
to minute pores in the stone itself, are somewhat lighter, though
giving equally strong concrete. They should weigh at least 120 pounds
per cubic foot. If the weight is less, there is probably too much fine
dust in the mixture.
The density and strength of concrete are also greatly improved by use
of a liberal amount of water. Enough water must be used to make the
concrete thoroughly soft and plastic, so as to quake strongly when
rammed. If mixed too dry it will never harden properly, and will be
light, porous, and crumbling.
Thorough mixing of concrete materials is essential, to increase the
density and give the cement used a chance to produce its full strength.
The cement, sand, and gravel should be intimately mixed dry, then the
water added and the mixing continued. If stone or coarse gravel is
added, this should be well wetted and thoroughly mixed with the mortar.
«Materials for Concrete Building Blocks.»—In the making of building
blocks the spaces to be filled with concrete are generally too narrow
to permit the use of very coarse material, and the {692} blockmaker is
limited to gravel or stone not exceeding 1/2 or 3/4 inch in size.
A considerable proportion of coarse material is, however, just as
necessary as in other kinds of concrete work, and gravel or screenings
should be chosen which will give the greatest possible density. For
good results, at least one-third of the material, by weight, should be
coarser than 1/8 inch. Blocks made from such gravel or screenings, 1
to 5, will be found as good as 1 to 3 with sand only. It is a mistake
to suppose that the coarse fragments will show on the surface; if the
mixing is thorough this will not be the case. A moderate degree of
roughness or variety in the surface of blocks is, in fact, desirable,
and would go far to overcome the prejudice which many architects hold
against the smooth, lifeless surface of cement work. Sand and gravel
are, in most cases, the cheapest material to use for block work. The
presence of a few per cent of clay or loam is not harmful provided the
mixing is thorough. Stone screenings, if of good quality, give fully
as strong concrete as sand and gravel, and usually yield blocks of
somewhat lighter color. Screenings from soft stone should be avoided,
also such as contain too much dust. This can be determined from the
weight per cubic foot, and by a sifting test. If more than two-thirds
pass 1/8 inch, and the weight (well jarred down) is less than 120
pounds, the material is not the best.
Cinders are sometimes used for block work; they vary greatly in
quality, but if clean and of medium coarseness will give fair results.
Cinder concrete never develops great strength, owing to the porous
character and crushability of the cinders themselves. Cinder blocks
may, however, be strong enough for many purposes, and suitable for work
in which great strength is not required.
«Lime.»—It is well known that slaked lime is a valuable addition to
cement mortar, especially for use in air. In sand mixtures, 1 to 4 or 1
to 5, at least one-third of the cement may be replaced by slaked lime
without loss of strength. The most convenient form of lime for use in
block-making is the dry-slaked or hydrate lime, now a common article of
commerce. This is, however, about as expensive as Portland cement, and
there is no great saving in its use. Added to block concrete, in the
proportion of 1/4 to 1/2 the cement used, it will be found to make
the blocks lighter in color, denser, and decidedly less permeable by
water.
«Cement.»—Portland cement is the only hydraulic material to be
seriously considered by the blockmaker. Natural and slag cements and
hydraulic lime are useful for work which remains constantly wet, but
greatly inferior in strength and durability when exposed to dry air.
A further advantage of Portland cement is the promptness with which
it hardens and develops its full strength; this quality alone is
sufficient to put all other cements out of consideration for block work.