1204TANNIC ACID
tains 3–4% ammonia, 2–5% phosphoric acid, and In mineral or chrome tanning, the sulfates of chro-
mium, aluminum, and zirconium are used (the last
0.50–1.00% potash.
two for white leather); here the reaction is of a
Hazard: Flammable, may ignite spontaneously.
coordination nature between the carboxyl groups of
Use: Fertilizer.
the skin collagen and the metal atom. Syntans are
also used; these are sulfonated phenol or naphthols
tannic acid. (gallotannic acid; described as a
condensed with formaldehyde. Condensation prod-
penta-(m-digalloyl)-glucose).
ucts other than phenol having strong hydrogen-
CAS: 1401-55-4. C
76
H
52
O
46
. Natural substance wide-
bonding power have been developed. Tannage by
ly found in nutgalls, tree barks, and other plant parts.
any method is a time-consuming and exacting pro-
Tannins are known to be gallic acid derivatives. A
cess, requiring careful control of pH, temperature,
solution of tannic acid will precipitate albumin. Tan-
humidity, and concentration factors.
nins are classified according to their behavior on dry
For further information refer to Tanners’ Council,
distillation into two groups, (1) condensed tannins,
University of Cincinnati, Cincinnati, Ohio. See
which yield catechol, and (2) hydrolyzable tannins,
leather.
which yield pyrogallol; (2) comprises two groups on
the basis of its products of hydrolysis, glucose, and
tantalic acid anhydride. See tantalum
(a) ellagic acid or (b) gallic acid.
oxide.
Properties: Lustrous, faintly yellowish, amorphous
powder, glistening scales, or spongy mass; darkens
tantalic chloride. See tantalum chloride.
on exposure to air; odorless; strong, astringent taste.
Mp decomposes at 210C. Soluble in water, alcohol,
tantalite. (Fe, Hg)(TaNb)
2
O
6
. The most impor-
and acetone; almost insoluble in benzene, chloro-
tant ore of tantalum, found in Canada, Africa, Brazil,
form, and ether. Flash p 390F (198C), autoign temp
Malaysia. When niobium content exceeds that of
980F (526C). Combustible.
tantalum, the ore is called columbite.
Derivation: Extraction of powdered nutgalls with
water and alcohol.
tantalum.
Grade: Technical, CP, NF, fluffy, FCC.
CAS: 7440-25-7. Ta. Element of atomic number 73
Hazard: Toxic by ingestion and inhalation.
in group VB of the periodic table, aw 180.9479,
Use: Chemicals (tannates, gallic acid, pyrogallic
valences of 2, 3, 5; no stable isotopes.
acid, hydrosols of the noble metals); alcohol denatu-
Properties: (1) Black powder. (2) Steel-blue-colored
rant; tanning; textiles (mordant and fixative); elec-
metal when unpolished, nearly a platinum-white
troplating; galvanoplastics (gelatin precipitant);
color when polished. D (1) 14.491, (2) 16.6 (worked
clarification agent in wine manufacture, brewing
metal), mp 2996C, bp 5425C, tensile strength of
and foods, writing inks; pharmaceuticals; deodori-
drawn wire may be as high as 130,000 psi, refr index
zation of crude oil; photography; paper (sizing, mor-
2.05, expansion coefficient 8 × 10
−6
over range
dant for colored papers); treatment of minor burns.
20–1500C. Electrical resistance 13.6 microhm-cm
(0C), 32.0 (500C). Soluble in fused alkalies; insolu-
tannin. Any of a broad group of plant-derived
ble in acids except hydrofluoric and fuming sulfuric
phenolic compounds characterized by their ability
acids.
to precipitate proteins. Some are more toxic than
Occurrence: Canada, Thailand, Malaysia, Brazil.
others, depending on their source. Those derived
Derivation: From tantalum potassium fluoride by
from nutgalls are believed to be carcinogens, while
heating in an electric furnace, by sodium reduction,
those found in tea and coffee may be virtually non-
or by fused salt electrolysis. The powdered metal is
toxic.
converted to a massive metal by sintering in a vacu-
See tannic acid.
um. Foot-long crystals can be grown by arc fusion.
Corrosion resistance: 99.5% pure tantalum is resis-
tanning. The preservation of hides or skins by use tant to all concentrations of hot and cold sulfuric
of a chemical that (1) makes them immune to bacte- acid (except concentrated boiling), hydrochloric
rial attack; (2) raises the shrinkage temperature; and acid, nitric and acetic acids, hot and cold dilute
(3) prevents the collagen fibers from sticking togeth- sodium hydroxide, all dilutions of hot and cold am-
er on drying, so that the material remains porous, monium hydroxide, mine and seawaters, moist sul-
soft, and flexible. Vegetable tanning is used mostly furous atmospheres, aqueous solutions of chlorine.
for sole and heavy-duty leathers. The chief vegeta- Grade: Powder 99.5% pure, sheet, rods, wire, ultra-
ble tannins are water extracts of special types of pure, single crystals.
wood or bark, especially quebracho and wattle. The Hazard: Dust or powder may be flammable. Toxic
main active constituent is tannic acid. The tannins by inhalation. TLV: 5 mg/m
3
.
penetrate the skin or hides after long periods of Use: Capacitors, chemical equipment, dental and sur-
soaking, during which the molecular aggregates of gical instruments, rectifiers, vacuum tubes, furnace
the tannin form cross-links between the polypeptide components, high-speed tools, catalyst, getter al-
chains of the skin proteins; hydrogen bonding is an loys, sutures and body implants, electronic circuitry,
important factor. thin-film components.