Minerals, Metals, and Other Materials
How is dry ice made?
Dry ice a solid form of carbon dioxide (CO2) used primarily to refrigerate perishables that are being transported from one location to another. The carbon dioxide, which at normal temperatures is a gas, is stored and shipped as a liquid in tanks that are pressurized at 1,073 pounds per square inch. To make dry ice, the carbon dioxide liquid is withdrawn from the tank and allowed to evaporate at a normal pressure in a porous bag. This rapid evaporation consumes so much heat that part of the liquid CO2 freezes to a temperature of –109°F (–78°C). The frozen liquid is then compressed by machines into blocks of “dry ice,” which will melt into a gas again when set out at room temperature.
It was first made commercially in 1925 by the Prest-Air Devices Company of Long Island City, New York, through the efforts of Thomas Benton Slate. It was used by Schrafft’s of New York in July 1925 to keep ice cream from melting. The first large sale of dry ice was made later in that year to Breyer Ice Cream Company of New York. Although used mostly as a refrigerant or coolant, other uses include medical procedures such as freezing warts, blast cleaning, freeze branding animals, and creating special effects for live performances and films.
Why is sulfuric acid important?
Sometimes called “oil of vitriol,” or vitriolic acid, sulfuric acid (H2SO4) has become one of the most important of all chemicals. It was little used until it became essential for the manufacture of soda in the eighteenth century. It is prepared industrially by the reaction of water with sulfur trioxide, which in turn is made by chemical combination of sulfur dioxide and oxygen by one of two processes (the contact process or the chamber process). Many manufactured articles in common use depend in some way on sulfuric acid for their production. Ninety percent of the sulfuric acid manufactured in the United States is used in the production of fertilizers and other inorganic chemicals.