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Explore the people, places, events, achievements, struggles and stories that shaped our journey.
Movements, leaders, victories and the continuing fight for equality.
Innovation, patents, science, technology and world-changing contributions.
Pioneers, champions, Negro Leagues, records, activism and excellence.
Meet the people whose lives, choices and achievements shaped the journey.
Black towns, communities, institutions and places where history happened.
Moments that changed communities, movements, institutions and the nation.
In August 1908, a white mob attacked Springfield, Illinois’s Black community, destroying homes and businesses and lynching two Black men. National outrage over the violence helped spur the movement that created the NAACP the following year.
MORE →Reflects the personal views, recollections, and perspective of the author, Mike Davis.
This is a personal recollection on the Move fire on May 13, 1985
The peptization of a liquid mixture is the process of converting the mixture into a colloid by shaking it with a suitable electrolyte called a peptizing agent.[1] That is, the insoluble solid particles which have settled out of the mixture (i.e. the precipitate) are reformed into microscopic particles suspended in the mixture. Peptization is the reverse of flocculation, the aggregation of colloidal particles into precipitate; as such, it is also known as deflocculation.
This is particularly important in colloid chemistry or for precipitation reactions in an aqueous solution. When colloidal particles bear a same sign electric charge, they mutually repel each other and cannot aggregate together. Freshly precipitated aluminium or iron hydroxide is extremely difficult to filter because the very fine colloidal particles directly pass through a paper filter. To facilitate the filtration, the colloidal suspension must be first flocculated by adding a concentrated solution of salt to the system. Multivalent cations are more efficient flocculants than monovalent cations: AlCl3 > CaCl2 > NaCl. The electrical charges present at the surface of the particles are so "neutralised" and disappear. More correctly speaking, the electrical double layer existing at the surface of the particles is compressed by the added electrolyte and collapses at high ionic strength. The electrical repulsion no longer hinders the aggregation of particles and they can then coalesce to form a flocculent precipitate that is easy to filter. If the precipitate is washed with an excessive volume of deionised water, the electrical double layer present at the surface of the particles expands again and the electrical repulsion reappears: the precipitate peptizes and the particles pass again through the filter.
Peptization is also used in nanoparticle synthesis to make a large grouping of particles split into many primary particles. This is done by changing the surface properties, applying a charge, or by adding a surfactant.
In the synthesis of titania (titanium dioxide) nanoparticles, peptization involves adsorption of quaternary ammonium cation on the titania surface. This causes the surface to become positively charged. Electrostatic repulsion of the primary particles in the agglomerated titania breaks up the agglomerate into primary particles.[2] The efficacy of adsorbates or suspension modification in imparting interparticle electrostatic repulsion is most commonly studied in terms of zeta potential.
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The peptization of a liquid mixture is the process of converting the mixture into a colloid by shaking it with a suitable electrolyte called a peptizing agent. That is, the insoluble solid particles which have settled out of the mixture (i.e. the precipitate) are reformed into microscopic particles suspended in the mixture. Peptization is the reverse of flocculation, the aggregation of colloidal particles into precipitate; as such, it is also known as deflocculation. This is particularly important in colloid chemistry or for precipitation reactions in an aqueous solution. When colloidal particles bear a same sign electric charge, they mutually repel each other and cannot aggregate together. Freshly precipitated aluminium or iron hydroxide is extremely difficult to filter because the very fine colloidal particles directly pass through a paper filter. To facilitate the filtration, the colloidal suspension must be first flocculated by adding a concentrated solution of salt to the system. Multivalent cations are more efficient flocculants than monovalent cations: AlCl3 > CaCl2 > NaCl. The electrical charges present at the surface of the particles are so "neutralised" and disappear. More correctly speaking, the electrical double layer existing at the surface of the particles is compressed by the added electrolyte and collapses at high ionic strength. The electrical repulsion no longer hinders the aggregation of particles and they can then coalesce to form a flocculent precipitate that is easy to filter. If the precipitate is washed with an excessive volume of deionised water, the electrical double layer present at the surface of the particles expands again and the electrical repulsion reappears: the precipitate peptizes and the particles pass again through the filter. Peptization is also used in nanoparticle synthesis to make a large grouping of particles split into many primary particles. This is done by changing the surface properties, applying a charge, or by adding a surfactant. In the synthesis of titania (titanium dioxide) nanoparticles, peptization involves adsorption of quaternary ammonium cation on the titania surface. This causes the surface to become positively charged. Electrostatic repulsion of the primary particles in the agglomerated titania breaks up the agglomerate into primary particles. The efficacy of adsorbates or suspension modification in imparting interparticle electrostatic repulsion is most commonly studied in terms of zeta potential.
Arsenic is a chemical element; it has the symbol As and atomic number 33. It is a metalloid and one of the pnictogens, and therefore shares many properties with its group 15 neighbors phosphorus and antimony. Arsenic is notoriously toxic. It occurs naturally in many minerals, usually in combination with sulfur and metals, but also as a pure elemental crystal. It has various allotropes, but only the grey form, which has a metallic appearance, is important to industry. The primary use of arsenic is in alloys of lead (for example, in car batteries and ammunition). Arsenic is also a common n-type dopant in semiconductor electronic devices, and a component of the III–V compound semiconductor gallium arsenide. Arsenic and its compounds, especially the trioxide, are used in the production of pesticides, treated wood products, herbicides, and insecticides. These applications are declining with the increasing recognition of the persistent toxicity of arsenic and its compounds. Arsenic containing compounds have been known since ancient times to be poisonous to humans. However, a few species of bacteria are able to use arsenic compounds as respiratory metabolites. Trace quantities of arsenic have been proposed to be an essential dietary element in rats, hamsters, goats, and chickens. Research has not been conducted to determine whether small amounts of arsenic may play a role in human metabolism. However, arsenic poisoning occurs in multicellular life if quantities are larger than needed. Arsenic contamination of groundwater is a problem that affects millions of people across the world. The United States' Environmental Protection Agency states that all forms of arsenic are a serious risk to human health. The United States Agency for Toxic Substances and Disease Registry ranked arsenic number 1 in its 2001 prioritized list of hazardous substances at Superfund sites. Arsenic is classified as a group 1 carcinogen.
Renewable energy (also called green energy) is energy made from renewable natural resources that are replenished on a human timescale. The most widely used renewable energy types are solar energy, wind power, bioenergy/biomass, and hydropower. Bioenergy and geothermal power are also significant in some countries. Renewable energy installations can be large or small and are suited for both urban and rural areas. Renewable energy is often deployed together with further electrification. This has several benefits: electricity can move heat and vehicles efficiently and is clean at the point of consumption. Variable renewable energy sources are those that have a fluctuating nature, such as wind power and solar power. In contrast, controllable renewable energy sources include dammed hydroelectricity, bioenergy, or geothermal power. For an energy to be renewable, it must be an endless source. Nuclear power is therefore not considered renewable, due to its reliance on non-renewable fuel. Renewable energy systems have rapidly become more efficient and cheaper over the past 40 years. A large majority of newly installed worldwide electricity capacity is now renewable. Renewable energy sources, such as solar and wind power, have seen significant cost reductions over the past decade, making them more competitive with traditional fossil fuels. In some geographic localities, photovoltaic solar or onshore wind is the cheapest new-build electricity. From 2011 to 2021, renewable energy grew from 20% to 28% of the global electricity supply. Power from the sun and wind accounted for most of this increase, growing from a combined 2% to 10%. Use of fossil energy shrank from 68% to 62%. In 2025, renewables accounted for 34% of global electricity generation, up from 32% in 2024, and are projected to reach over 43% by 2030. Many countries already have renewables contributing more than 20% of their total energy supply, with some generating over half or even all their electricity from renewable sources. The main motivation to use renewable energy instead of fossil fuels is to reduce greenhouse gas emissions, which cause climate change. In general, renewable energy sources pollute much less than fossil fuels. Renewables also cause much less air pollution than fossil fuels, improving public health, and are less noisy. The International Energy Agency estimates that to achieve net zero emissions by 2050, 90% of global electricity will need to be generated by renewables. The current pace of renewable expansion remains far from this required rate globally, including in major economies with high financial capacities such as the G7 and the EU. The deployment of renewable energy still faces obstacles, especially fossil fuel subsidies, lobbying by incumbent power providers, and local opposition to the use of land for renewable installations. Like all mining, the extraction of minerals required for many renewable energy technologies also results in environmental damage. Some also consider nuclear power a renewable power source, although this is controversial, as nuclear energy requires mining uranium, a nonrenewable resource.
Sodium hydroxide, also known as caustic soda and, more generically, as lye, is an inorganic compound with the formula NaOH. It is a white solid ionic compound consisting of sodium cations Na+ and hydroxide anions OH−. As a strong nucleophile, it is frequently used in SN2 reactions. Sodium hydroxide is a highly corrosive base and alkali that decomposes lipids and proteins at ambient temperatures, and may cause severe chemical burns at high concentrations. It is highly soluble in water, and readily absorbs moisture and carbon dioxide from the air. It forms a series of hydrates NaOH·nH2O. The monohydrate NaOH·H2O crystallizes from water solutions between 12.3 and 61.8 °C. The commercially available "sodium hydroxide" is often this monohydrate, and published data may refer to it instead of the anhydrous compound. As one of the simplest hydroxides, sodium hydroxide is frequently used alongside neutral water and acidic hydrochloric acid to demonstrate the pH scale to chemistry students. Sodium hydroxide is used in many industries: in the making of wood pulp and paper, textiles, drinking water, soaps and detergents, and as a drain cleaner. Worldwide production in 2022 was approximately 83 million tons.
Before the 1921 destruction of Tulsa’s Greenwood District, Black residents had created a remarkable center of business and community life. The district included stores, professional offices, entertainment venues and homes owned by Black citizens. Understanding Greenwood means learning what was built—not only what was burned.
MORE →Shirley Chisholm, elected in 1968.