Early 20th century

In 1907 an amendment to the Public Healtii Act 1875 extended the requirements for local authorities to collect trade refuse and also allowed them to charge for its removal. At this time tiie nature of waste began to change and the use of disposable items and packaging started to develop with such things 

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Since the early 20th century, chemists have represented molecular information by molecular models. The human brain comprehends these representations of graphical models with 3D relationships more effectively than numerical data of distances and angles in tabular form. Thus, visualization makes complex information accessible to human understanding easily and directly through the use of images. 

The specification of wires can be confusing. All wires diameters are based upon the American Wire Gauge (AWG) table, published in the early 20th century. The metric countries directly converted these dimension (inches) to millimeters and created what is now the lEC R20 wire table. This is shown below in both measurement systems in Table F-t. 

Two marks of the acceptance of the new discipline, physical chemistry, in the early 20th century were the Nobel prizes for its three founders and enthusiastic... 

Natural rubber can be obtained from the sap of a number of plants and trees, the most common source is the Hevea brasiliensis tree. Although natural rubber was known in Central and South America before the arrival of Christopher Columbus in 1492, the first use as an adhesive was established in a patent dated in 1891. As rubber became an important part of the industrial revolution, the rubber adhesives market grew in importance. To comply with the increasing demand on natural rubber materials, plantations of Hevea brasiliensis trees were established in southeast Asia in the early 20th Century, mainly to supply the demand from the automobile industry. 

Determining the structure of an organic compound was a difficult and time-consuming process in the 19th and early 20th centuries, but powerful techniques are now available that greatly simplify the problem. In this and the next chapter, we ll look at four such techniques—mass spectrometry (MS), infrared (IR) spectroscopy, ultraviolet spectroscopy (UV), and nuclear magnetic resonance spectroscopy (NMR)—and we U see the kind of information that can be obtained from each. 

Even before a new organic substance has its structure determined, it must be purified by separating it from solvents and all contaminants. Purification was an enormously time-consuming, hit-or-miss proposition in the 19th and early 20th centuries, but powerful instruments developed in the last few decades now simplify the problem. 

Since ancient times, the light emitted by fireflies and glow-worms has attracted the curiosity of people. Descriptions of the phenomena are frequently found in old poems, songs and folklores of many countries. Old scientific studies of these phenomena are also numerous, particularly after the 17th century. However, the chemical study was not begun until the early 20th century. 

If an electron is transferred from a reducing agent to an arenediazonium ion, an aryldiazenyl radical (8.47) is formed. As discussed in this section, the latter dissociates rapidly into an aryl radical and N2 (Scheme 8-28). This type of dediazoniation was observed by Griess (1864 c), albeit not in our present formulation. He found that arenediazonium ions formed iodoarenes and N2 in the presence of iodide ions. More important for synthetic organic chemistry were some dediazonia-tions discovered in the late 19th and early 20th centuries, which are catalyzed by metals and metal ions, namely the Sandmeyer, Pschorr, Meerwein, and related syntheses (see Ch. 10). 

Fig. 11. Forage production of grassland ecosystems subject to initial overgrazing (early 20th century, degree of production estimated) and subsequent invasion by the alien grass, Eragrostis lehmanniana (after Morton, 1985).

Szulakowska, Urszula. The tree of Aristotle images of the Philosophers Stone and their transference in alchemy from the 15th to the early 20th century. Ambix 33, no. 2/3 (Jul/Dec 1986) 53-77. 

World Pb production continued to increase in the early 20th century (Fig. 9.4), but then slowed in the latter part of the 20th century due to discontinuing Pb additives to gasoline. 

Auger A process for chlorinating benzene to chlorobenzene, catalyzed by metallic iron. Invented by V.E. Auger in 1916 and operated in France and Italy in the early 20th century. 

The process was invented in Germany by C. Lowig in 1882 and used at Joseph Croslield Sons, Warrington, UK, in the late 19th and early 20th centuries. See also causticization. 

The concept of activity was introduced in the early 20th century by one of the giants of American chemistry, G. N. Lewis. 

Suggestions made in the early 20th Century that obsidian found on the island of Malta (with no natural sources) might have been brought there by Minoan traders were supported by the findings of Cornaggia Castiglioni et al. (1963). 

Finally, in the early 20th century Albert Einstein explained the photoelectric effect based on quantized packets of electromagnetic radiation called photons. These quickly led to the familiar relationships of the energy of a photon,... 

Those trying to further improve rosin-based technologies in constant evolution since the early 20th century. 

Shock Therapy. The early 20th century saw the development of the first effective biological treatments for depression, the shock therapies. The first shock treatments used injection of horse serum or insulin. A major advance in treatment occurred with the advent of electroconvulsive therapy (ECT) in 1934. Although initially used to treat schizophrenia, ECT was soon found to be highly effective for other psychiatric disorders including depression and mania. ECT remained the primary biological psychiatric treatment until the widespread release of psychiatric medications in the 1950s. 

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