Qualifying Child. To be considered a qualifying child, your grandchild must be under the age of 19 on the last day of the tax year, or if he's a full-time student, under the age of 24.No age restrictions apply, however, if your grandchild is permanently and totally disabled.ualifying Child. To be considered a qualifying child, your grandchild must be under the age of 19 on the last day of the tax year, or if he's a full-time student, under the age of 24.
Platinum-iridium alloy. Platinum-iridium alloys are alloys of the platinum group precious metals platinum and iridium. Typical alloy proportions are 90:10 or 70:30 (Pt:Ir). These have the chemical stability of platinum, but increased hardness. The Vickers hardness of pure platinum is 56 HV while platinum with 50% of iridium can reach over 500 HV.
Iridium and osmium were identified in the black residue remaining after dissolving platinum ore with aqua regia, a mixture of 25% nitric acid (HNO 3) and 75% hydrochloric acid (HCl). Today, iridium is still obtained from platinum ores and as a by-product of mining nickel.Pure iridium is very brittle and is nearly impossible to machine. It is primarily used as a hardening agent for platinum.Platinum-iridium alloys are used to make crucibles and other high temperature equipment. Iridium is also alloyed with osmium to make the tips of fountain pens and compass bearings.Iridium is the most corrosive resistant metal known.ure iridium is very brittle and is nearly impossible to machine. It is primarily used as a hardening agent for platinum. Platinum-iridium alloys are used to make crucibles and other high temperature equipment.