Classical elements

The a-helix is the classic element of protein structure. A single a-helix can order as many as 35 residues whereas the longest strands include only about 15 residues, and one helix can have more influence on the stability and organization of a protein than any other individual structure element. a-Helices have had an immense influence on our understanding of protein structure because their regularity makes them the only feature readily amenable to theoretical analysis. 

The great technical and economic Tmportance of this product group was reached despite its higher price only because of its special properties. Due to the ionic sulfate group and the adjacent ether groups, ether sulfates combine the classical elements of ionic and nonionic surfactants in one molecule. This provides a number of properties, one of which, the Krafft-Point, is of special importance for the technical application of these compounds. 

What this really means is that the classical elements are familiar representatives of the different states that matter can... 

Some scholars have identified Jabir s sulphur and mercury with the Aristotelian opposites fire and water. One thing is sure they are not the yellow sulphur and the glistening, fluid mercury of the chemistry laboratory, which were known in more or less pure form even to the alchemists. Instead, these two principles were rather like the four classical elements ideal substances embodied only imperfectly in earthly materials. 

So the Jabirian system embraced the four classical elements and then buried them, just as the Aristotelian elements allowed but ignored the universalhyle. It marks the beginning of a tendency to pay lip service to Aristotle while getting on with more practical concerns about what things are made of. 

Ancient philosophers in Greece, India, China, and Japan speculated that all matter was composed of four or five elements. The Greeks thought that these were fire, air, earth, and water. Indian philosophers and Aristotle from Greece also thought a fifth element—"aether" or "quintessence"—filled all of empty space. The Greek philosopher Democritus thought that matter was composed of indivisible and indestructible atoms. These concepts are now known as classical elements and classical atomic theory. 

Robert Boyle was educated in alchemy in the mid-1600s, but he published a book called The Skeptical Chemist that attacked alchemy and advocated using the scientific method. He is sometimes called the founder of modern chemistry because of his emphasis on proving a theory before accepting it, but the birth of modern chemistry is usually attributed to Lavoisier. Boyle rejected the 4 classical elements and proposed the modern definition of an element. Boyle s law states that gas volume is proportional to the reciprocal of pressure. 

Classic Elemental Analysis Procedures and Isotope Ratio Mass Spectrometry... 

The isotopic characterisation of organic compounds by classical elemental analysis with isotope ratio mass spectrometry (EA-IRMS) demands milligram amounts of pure compounds, which can not always easily be provided. Most analytes in flavour characterisation are volatile, and therefore, after their extraction, coupling of (capillary) gas chromatography (cGC) with IRMS would be an ideal tool for the isotope ratio analysis of the individual substances. For C- ]127, 128] and N-analysis ]179, 180] this has been realised for a long time by combining GC to IRMS via a combustion (C) unit (GC-C-IRMS), even for polar substances after their derivatisation ]181, 182]. 

Since neither model adequately describes the behavior of real viscoelastic materials, a combination of the classic elements is often made to gain closer representation. The most common configuration is called the standard linear solid4 configuration, and it is illustrated in Figure 6.6. A more accurate representation of actual behavior can be obtained by a composite of multiple elements of the standard linear solid configuration into a multi-element model (Figure 6.7) with an array of coefficients for each element. 

At one time GC analysis was less accurate than classical elemental analysis, but the development of simple, reliable and sensitive thermal conductivity detectors (TCDs), special electronic integrators and small computers has brought the reproducibility of chromatographic peak-area measurements to at least 0.2% (see, for example, ref. 11) the accuracy of chromatographic elemental analysis is now close to that of standard gravimetric methods, which is normally 0.3% [12]. If the GC elemental analysis is used for the determination of reactive compounds, such as halogens or hydrogen halides, use is made of gas density balances in which the sensitive elements are protected by a flow of an inert gas [13]. 

The determination of the C H ratio for identification purposes is practicable only if it is performed with a high degree of accuracy. It should be remembered for comparison that the accuracy of classical elemental analysis methods is about 0.3%, which is insufficient for the identification of organic compounds. For example, an absolute error of... 

Empedocles (495-435 BC) Greek pre-Socratic philosopher and a citizen of Agrigentum, a Greek city in Sicily he is best known for being the origin of the cosmogenic theory of the four classical elements. 

Not surprisingly, people had speculated on the nature of heat since ancient times. Fire was one of the four classical elements and hotness one of the four primary qualities. At the time of the scientific revolution there was a widespread belief that heat was a substance, and some held the view that it was composed of atoms. Francis Bacon, Robert Boyle and Robert Hooke adopted a particulate explanation, and Hooke held the view that a body became hot because of the motion of the particles of which it is composed. 

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