Phytolith

Phytoliths (from Greek, "plant stone") are rigid, microscopic structures made of silica, found in some plant tissues and persisting after the decay of the plant. These plants take up silica from the soil, whereupon it is deposited within different intracellular and extracellular structures of the plant. Phytoliths come in varying shapes and sizes. Although some use "phytolith" to refer to all mineral secretions by plants, it more commonly refers to siliceous plant remains. In contrast, mineralized calcium secretions in cacti are composed of calcium oxalates.

Functions

There is still debate in the scientific community as to why plants form phytoliths, and whether silica should be considered an essential nutrient for plants. Studies that have grown plants in silica-free environments have typically found that plants lacking silica in the environment do not grow as well. For example, the stems of certain plants will collapse when grown in soil lacking silica. In many cases, phytoliths appear to lend structure and support to the plant, much like the spicules in sponges and leather corals. Phytoliths may also provide plants with protection. These rigid silica structures help to make plants more difficult to consume and digest, lending the plant's tissues a grainy or prickly texture. Phytoliths also appear to provide physiologic benefits. Experimental studies have shown that the silicon dioxide in phytoliths may help to alleviate the damaging effects of toxic heavy metals, such as aluminum. Finally, calcium oxalates serve as a reserve of carbon dioxide. Cacti use these as a reserve for photosynthesis during the day when they close their pores to avoid water loss; baobabs use this property to make their trunks more flame-resistant.

Hydrochloric acid

Hydrochloric acid is a clear, colorless, highly pungent solution of hydrogen chloride (HCl) in water. It is a highly corrosive, strong mineral acid with many industrial uses. Hydrochloric acid is found naturally in gastric acid. When it reacts with an organic base it forms a hydrochloride salt.

It was historically called acidum salis, muriatic acid, and spirits of salt because it was produced from rock salt and green vitriol (by Basilius Valentinus in the 15th century) and later from the chemically similar substances common salt and sulfuric acid (by Johann Rudolph Glauber in the 17th century). Free hydrochloric acid was first formally described in the 16th century by Libavius. Later, it was used by chemists such as Glauber, Priestley, and Davy in their scientific research.

With major production starting in the Industrial Revolution, hydrochloric acid is used in the chemical industry as a chemical reagent in the large-scale production of vinyl chloride for PVC plastic, and MDI/TDI for polyurethane. It has numerous smaller-scale applications, including household cleaning, production of gelatin and other food additives, descaling, and leather processing. About 20 million tonnes of hydrochloric acid are produced worldwide annually.

Alto saxophone

The alto saxophone, also referred to as the alto sax, is a member of the saxophone family of woodwind instruments invented by Belgian instrument designer Adolphe Sax in the 1840s, and patented in 1846. It is smaller than the tenor but larger than the soprano. The alto and tenor are the most common types of saxophones. The alto saxophone is commonly used in classical music (such as concert bands, chamber music, and solo repertoire), military bands, marching bands, and jazz (such as big bands, jazz combos, swing music, etc. The saxophone fingerings are all universal, so a saxophone player can play any type of saxophone.

Type

The alto saxophone is an E♭ transposing instrument and reads the treble clef. A written C-natural sounds a major sixth lower (concert E♭) when played. Because the alto saxophone is a reed instrument, it is classified as a woodwind instrument.

Range

The range of the alto saxophone is from concert D♭₃ (the D♭ below middle C—see Scientific pitch notation) to concert A♭₅ (or A₅ on altos with a high F♯ key). As with most types of saxophones, the standard written range is B♭₃ to F₆ (or F♯₆). Above that, the altissimo register begins at F♯ and extends upwards. The saxophone's altissimo register is more difficult to control than that of other woodwinds and is usually only expected from advanced players. By covering or partially covering the bell of the saxophone when playing B♭₃, it is possible for the alto saxophone to reach A₃ as well.

Nitric acid

Nitric acid (HNO₃), also known as aqua fortis and spirit of niter, is a highly corrosive mineral acid.

The pure compound is colorless, but older samples tend to acquire a yellow cast due to decomposition into oxides of nitrogen and water. Most commercially available nitric acid has a concentration of 68% in water. When the solution contains more than 86% HNO₃, it is referred to as fuming nitric acid. Depending on the amount of nitrogen dioxide present, fuming nitric acid is further characterized as white fuming nitric acid or red fuming nitric acid, at concentrations above 95%.

Nitric acid is the primary reagent used for nitration – the addition of a nitro group, typically to an organic molecule. While some resulting nitro compounds are shock- and thermally-sensitive explosives, a few are stable enough to be used in munitions and demolition, while others are still more stable and used as pigments in inks and dyes. Nitric acid is also commonly used as a strong oxidizing agent.

Physical and chemical properties