of sulfuric acid produced by the lead chamber process, chamber acid being the acid produced in the lead chamber itself (<70% to avoid contamination with nitrosylsulfuric acid) and tower acid being the acid recovered from the bottom of the Glover tower. They are now obsolete as commercial concentrations of sulfuric acid, although they may be prepared in the laboratory from concentrated sulfuric acid if needed. In particular, "10 M" sulfuric acid (the modern equivalent of chamber acid, used in many titrations), is prepared by slowly adding 98% sulfuric acid to an equal volume of water, with good stirring: the temperature of the mixture can rise to 80 °C (176 °F) or higher. Pure sulfuric acid Pure sulfuric acid contains not only molecules, but is actually an equilibrium of many other chemical species, as it is shown in the table below. Pure sulfuric acid is a colorless oily liquid, and has a vapor pressure of <0.001 mmHg at 25 °C and 1 mmHg at 145.8 °C, and 98% sulfuric acid has a <1 mmHg vapor pressure at 40 °C. In the solid state, sulfuric acid is a molecular solid that forms monoclinic crystals with nearly trigonal lattice parameters. The structure consists of layers parallel to the (010) plane, in which each molecule is connected by hydrogen bonds to two others. Hydrates are known for n = 1, 2, 3, 4, 6.5, and 8, although most intermediate hydrates are stable against disproportionation. Polarity and conductivity Anhydrous is a very polar liquid, having a dielectric constant of around 100. It has a high electrical conductivity, caused by dissociation through protonating itself, a process known as autoprotolysis. 2 H2SO4 <=> H3SO4+ + HSO4- The equilibrium constant for autoprotolysis is The comparable equilibrium constant for water, Kw is 10−14, a factor of 1010 (10 billion) smaller. In spite of the viscosity of the acid, the effective conductivities of the and ions are high due to an intramolecular proton-switch mechanism (analogous to the Grotthuss mechanism in water), making sulfuric acid a good conductor of electricity. It is also an excellent solvent for many reactions. Chemical properties Reaction with water and dehydrating property Because the hydration reaction of sulfuric acid is highly exothermic, dilution should be performed by adding the acid to the water rather than the water to the acid, to avoid acid splashing. Because the reaction favors the rapid protonation of water, addition of acid