The overall chemical and structural composition is used to divide ambers into five classes.

Its chemical composition makes it difficult to match the amber to its producers – it is most similar to the resins produced by flowering plants ; however, there are no flowering plant fossils until the Cretaceous, and they were not common until the Upper Cretaceous.

Amber is a unique preservational mode, preserving otherwise unfossilizable parts of organisms ; as such it is helpful in the reconstruction of ecosystems as well as organisms ; the chemical composition of the resin, however, is of limited utility in reconstructing the phylogenetic affinity of the resin producer.

Lavoisier also contributed to early ideas on composition and chemical changes by stating the radical theory, believing that radicals, which function as a single group in a chemical process, combine with oxygen in reactions.

Depending on the chemical composition of the adhesive, they will adhere to different materials to greater or lesser degrees.

This definition was proposed by Justus von Liebig circa 1838, based on his extensive works on the chemical composition of organic acids.

Subsequently, atom probe has been used in the analysis of the chemical composition of a wide range of alloys.

Later it was found at Montebras, Creuse, France, and at Hebron in Maine ; and because of slight differences in optical character and chemical composition the names montebrasite and hebronite have been applied to the mineral from these localities.

The exact chemical composition and the sequence in which these units are arranged is called the primary structure, in the case of proteins.

These domains reflect whether the cells have nuclei or not, as well as differences in the chemical composition of the cell exteriors and ribosomes.

Translucent Bakelite jewelry, poker chips and other gaming items such as chess sets were also introduced in the 1940s under the Prystal Corporation name, however, its basic chemical composition remained the same.

Chemistry is the science of matter, its properties, structure, composition and its changes during interactions and chemical reactions.

Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties.

A compound is a substance with a particular ratio of atoms of particular chemical elements which determines its composition, and a particular organization which determines its chemical properties.

A chemical substance is a kind of matter with a definite composition and set of properties.

* Analytical chemistry is the analysis of material samples to gain an understanding of their chemical composition and structure.

* Organic chemistry is the study of the structure, properties, composition, mechanisms, and chemical reaction of organic compounds.

Collagen is a composed of a triple helix, which generally consists of two identical chains ( α1 ) and an additional chain that differs slightly in its chemical composition ( α2 ).

While rocks melted by the impact resemble volcanic rocks, they incorporate unmelted fragments of bedrock, form unusually large and unbroken fields, and have a much more mixed chemical composition than volcanic materials spewed up from within the Earth.

* μ < sub > e </ sub > is the average molecular weight per electron, which depends upon the chemical composition of the star.

Chemistry – science of atomic matter ( matter that is composed of chemical elements ), especially its chemical reactions, but also including its properties, structure, composition, behavior, and changes as they relate the chemical reactions.

The importance of knowing in what chemical forms the hormone may exist is accentuated by the recent observation that there exists an abnormally long-acting TSH in blood drawn from many thyrotoxic patients ( Adams, 1958 ).

Experiments have been conducted to attempt the synthesis of ununennium ( Uue ), which is likely to be the next member of the group, but they have all met with failure .< ref name =" link "> However, ununennium may not be an alkali metal due to relativistic effects, which are predicted to have a large influence on the chemical properties of superheavy elements.

" While chemical issues in the brain that result in anxiety ( especially resulting from genetics ) are well documented, this study highlights an additional environmental factor that may result from being raised by parents suffering from chronic anxiety.

In chemical terms, proline is, therefore, an imino acid, since it lacks a primary amino group, although it is still classed as an amino acid in the current biochemical nomenclature, and may also be called an " N-alkylated alpha-amino acid ".

Antibacterials such as metronidazole, tinidazole, cephamandole, latamoxef, cefoperazone, cefmenoxime, and furazolidone, cause a disulfiram-like chemical reaction with alcohol by inhibiting its breakdown by acetaldehyde dehydrogenase, which may result in vomiting, nausea, and shortness of breath.

Adhesion, the attachment between adhesive and substrate may occur either by mechanical means, in which the adhesive works its way into small pores of the substrate, or by one of several chemical mechanisms.

coloured marker, chemical, nuclear devices ; high explosive anti-tank ( HEAT ) and canister may be considered special types of bursting shell.

A chemical reaction between the carbonate and hydrochloric acid may produce carbon dioxide gas.

A positive test indicates that the chemical is mutagenic and therefore may act as a carcinogen, since cancer is often linked to mutation.

It may involve chemical tests, physical tests, or performance tests.

In systems engineering it may involve black-box testing performed on a system ( for example: a piece of software, lots of manufactured mechanical parts, or batches of chemical products ) prior to its delivery.

Boba pearls, milk powder, and juice syrups may contain banned chemical additives in order to reduce costs.

Like some of the chemical weapons, biological weapons may also be useful as area denial weapons.

Though herbicides are chemicals, they are often grouped with biological warfare and chemical warfare because they may work in a similar manner as biotoxins or bioregulators and also because the Army Biological Laboratory tested them and the Army's Technical Escort Unit which all chemical, biological, radiological ( nuclear ) materials.

Membranes in cells typically define enclosed spaces or compartments in which cells may maintain a chemical or biochemical environment that differs from the outside.

The type of chemical reactions a substance may undergo and the energy changes that may accompany it are constrained by certain basic rules, known as chemical laws.

Strictly speaking, a mixture of compounds, elements or compounds and elements is not a chemical substance, but it may be called a chemical.

Thus, all carbon isotopes have nearly identical chemical properties because they all have six protons and six electrons, even though carbon atoms may differ in number of neutrons.

These may involve a combination of chemical processes, erosion from water, tectonic forces, microorganisms, pressure, atmospheric influences, and even digging.

A catalyst may participate in multiple chemical transformations.