Pencil sharpener pencil in position, although they then sharpen them to the usual conical point as for a round pencil, abandoning some distinctive aspects of the carpenter's pencil. Sharpeners with a single blade for use on wax crayons are available, and sometimes included in boxes of crayons. These often have plastic blades, which are adequate for the soft wax. Mechanical pencils dispense the graphite lead progressively during use and thus do not require sharpening; such pencils are sometimes called "self-sharpening". A type of mechanical pencil has a rotating gear mechanism which rotates the lead slightly every time the lead is lifted off
Lead tetrachloride Lead tetrachloride Lead tetrachloride, also known as lead(IV) chloride, has the molecular formula PbCl. It is a yellow, oily liquid which is stable below 0 °C, and decomposes at 50 °C. It has a tetrahedral configuration, with lead as the central atom. The Pb–Cl covalent bonds have been measured to be 247 pm and the bond energy is 243 kJ⋅mol. Lead tetrachloride can be made by reacting lead(II) chloride PbCl, and hydrochloric acid HCl, in the presence of chlorine gas (Cl), leading to the formation of chloroplumbic acid HPbCl. It is then converted to the ammonium salt (NH)PbCl by adding