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Argon plasma coagulation (APC) is an electrosurgical procedure in which electrical energy in the form of ionized argon gas is transferred to target tissue. The APC device uses non-contact thermal energy in the form of ionized gas or plasma for coagulation of the tissue. This technique was first used in open surgical and laparoscopic procedures nearly 2 decades ago. With the development of flexible probes and special electrical waveforms in 1990s, APC has been adopted for use in flexible endoscopy for the treatment of various gastrointestinal conditions. APC is an efficacious, safe, and easy-to-use method of hemostasis and devitalization of tissues. This chapter will discuss the indications and contraindications for APC, provide a detailed step-by-step description of the procedure, and an evidence-based review of the procedure. [ABSTRACT FROM AUTHOR]

Keep up your bright swords, for the dew will rust them. Water is the most common substance on Earth, and it no doubt has the best known of all chemical formulas: H2O. It is one of only two liquids that occur naturally in appreciable quantities, the other example being petroleum. More than three quarters of the Earth's surface is covered with water, and if it were not for this compound, there would be no life. About 60% of the weight of the human body is water, it being present in the interior of every cell. It also accounts for the bulk of such specialized aqueous media as blood and mucous. The central role played by water was of course clear from the earliest times, and Aristotle regarded it as one of the four elements, together with air, fire and earth. Its chemical structure became clear in the late eighteenth century, when Henry Cavendish and Antoine Lavoisier established that it is a combination of hydrogen (discovered by Cavendish in 1766) and oxygen (discovered by Joseph Priestley in 1774). Cavendish burned measured quantities of these two gases together and found that they produced water, no change in total weight having occurred during the reaction. The reverse process, decomposition of water into hydrogen and oxygen, was first achieved by Lavoisier. In spite of its abundance and apparent simplicity, water is an unusual compound, and compared with other liquids we could call it exotic. [ABSTRACT FROM AUTHOR]

The force of nature could no farther go; to make a third she join'd the former two. Most substances are mixtures of two or more elements, and chemical compounds are found to have definite compositions. They are also found to consist of molecules, which are the smallest particles that can exist in the free state and still retain the characteristics of the substance. Thus the chemical formula for water is always H2O, indicating that its molecules contain two hydrogen atoms and one oxygen. (The subscript 1 is not written explicitly; H2O implies H2O1.) The formula H2O2, in which the relative proportions of hydrogen and oxygen are different from those in water, belongs to a different chemical compound, the common bleaching agent hydrogen peroxide. Similarly, sodium chloride, also known as common salt, has the formula NaCl, and not Na2Cl or NaCl3. This shows that the forces that hold atoms together in groups must have certain characteristics which determine the rules of combination. The occurrence of chemical reactions reveals that the forces can be overcome, allowing the atoms to move apart and establish bonds with other atoms. A simple example of such an event is the reaction Zn + 2HCl → ZnCl2 + H2 in which the addition of hydrochloric acid to zinc produces zinc chloride and hydrogen, which is liberated as a gas. This demonstrates that the binding forces between zinc and chlorine atoms are stronger than those which hold hydrogen to chlorine. [ABSTRACT FROM AUTHOR]

Chapter 12 of the book "2005 ASHRAE Handbook—Fundamentals" is presented. It explores the types and levels of air contaminants which might enter ventilation system and be considered as indoor contaminants. It discusses major gaseous components of clean air like oxygen, nitrogen, argon, and carbon dioxide as well as possible problems in the indoor environment like allergens, tobacco smoke, and formaldehyde.