691 INTERCALATION
and related professions in industry, academia and e.g., polystyrene, PVC, cellulose, glass, magnesia,
government. The Institute advances the science and and aluminum silicate.
technology of food through the exchange of knowl- Air is a unique case, as it is the only gaseous material
edge. Itsa world headquarters are at 221 N. LaSalle in actual use as an insulator. Its dielectric constant is
St., Ste. 300, Chicago, IL 60601-1291. Website: 1.0058, far less than that of any other dielectric
HTTP://www.ift.org. material, and it has low thermal conductivity as well.
It is particularly effective when trapped within a
solid network, as in wool, cellular plastics, or glass
instrument. Any of a wide variety of devices
fibers, or as an interlayer between wall panels.
used for one of the following purposes: (1) observa-
tion (microscope); (2) measurement (thermometer,
thermocouple, flowmeter, balance); (3) chemical
insulin. A polypeptide hormone having a molecu-
analysis (spectrometer). lar weight of 5733. It is formed in the isles of Lan-
See analytical chemistry; instrumentation. gerhans located in the pancreas and was so named
for this reason. Insulin is composed of 16 amino
acids arranged in a coiled chain and cross-linked in
instrumentation. (1) Plant. An inclusive term
several places by the disulfide bonds of cystine resi-
for sensing devices that measure, record, and control
dues. The sequence of amino acids has been eluci-
temperature, flow rate, thickness, pH, liquid level,
dated. The insulin molecule was synthesized in
and other process variables on a continuous basis.
1963. In 1977, rat insulin was produced in the bacte-
Some types, e.g., thickness gauges, utilize radioiso-
rium E. coli by recombinant DNA techniques. A
topes. Particularly sophisticated computerized in-
year later human insulin was generated after chemi-
strumentation is required in petroleum refining and
cally synthesized genes were added to E. coli. This
nuclear reactor control. (2) Laboratory. A broad
synthetic insulin is now in commercial production
range of analytical techniques and devices utilized
and has been approved by FDA. Insulin regulates
in the many types of chromatography and spectros-
carbohydrate metabolism in the body by decreasing
copy. Significant advances in analytical instrumen-
the blood glucose level. A systemic deficiency leads
tation have been made in recent years, e.g., in liquid
to diabetes.
chromatography (HPLC). A notable event in this
Properties: White powder or hexagonal crystals.
field is the annual Pittsburgh Conference on Analyt-
Readily soluble in dilute acids; soluble in water.
ical Chemistry and Applied Spectroscopy. (3) Gen-
Derivation: Extraction of minced pancreas with
eral. Of special significance for both laboratory and
acidified dilute alcohol, followed by precipitation
process control is the introduction of fiber optical
with absolute alcohol; also by gene-splicing
devices that can transmit signals from many remote
methods.
locations. They are particularly useful in analyzing
Grade: USP, in various solutions or suspensions that
samples of radioactive chemicals and other hazard-
include insulin injection; isophane insulin suspen-
ous materials. They are also used in high-tempera-
sion; protamine zinc insulin suspension; NF, as glo-
ture thermometry and dosimetry.
bin zinc insulin injection.
See fiber, optical.
Hazard: Overdosage can be fatal.
Use: Medicine (for diabetes control).
insulating oil. See transformer oil.
See Banting; recombinant DNA.
insulator. Any substance or mixture that has an
integral membrane proteins. Proteins in-
extremely low dielectric constant, low thermal con-
serted into a membrane by hydrophobic interac-
ductivity, or both. Electrical insulators are either
tions. Contrast with peripheral proteins.
solid or liquid, the latter being used in transformers
(askarel, mineral oils, silicone oils). A wide variety
intercalating mutagen. A mutagen that inserts
of solid types includes porcelains, glass, mica, alu-
itself between two successive bases in a nucleic acid
mina, various high polymers (epoxies, polyethyl-
causing a frame-shift mutation.
ene, polystyrene, phenolics), cellulosic materials,
nylon, and silicone resins. All these may be used
alone or combined with other insulators as compos-
intercalation compound. A compound com-
ites. posed of a crystalline lattice that acts as an electron
See dielectric; transformer oil. donor, and “foreign” electron acceptor atoms inter-
Thermal insulators comprise an equally broad range spersed or diffused between the planes of the lattice.
of materials. Such inorganics as mineral fibers, An important group of intercalated compounds are
magnesia, aluminum silicate, cellulose, and glass composed of graphite, where bromine, for example,
fibers are widely used for steam and hot-water pipes, can act as electron acceptor. Graphite is particularly
furnaces, and blown-in home insulation. Organic susceptible to this phenomenon because of its order-
products that are effective include plastic foams ly stacked layers of crystals. Anhydrous metal ni-
(polyurethane, polyvinyl chloride, polystyrene) and trates such as copper and zinc nitrates also form
cellular rubber. There are a number of materials that intercalated compounds with graphite. A further ex-
may be called double insulators, since they have ample is trilithium nitride, whose structure consists
both electrical and thermal insulating properties, of a series of layers of dilithium nitride, between