Atmospheres, inert

Used (particularly He, Ar) to provide an inert atmosphere, e.g. for welding, and in electric light bulbs, valves and discharge tubes (particularly Ne). Liquid He is used in cryoscopy. The amounts of He and Ar formed in minerals by radioactive decay can be used to determine the age of the specimen. Xe and to a lesser extent Kr and Rn have a chemistry the other noble gases do not form chemical compounds. 

Sodium metal should be handled with great care. It cannot be maintained in an inert atmosphere and contact with water and other substances with which sodium reacts should be avoided. 

The effectiveness of phenoHc inhibitors is dependent on the presence of oxygen and the monomers must be stored under air rather than an inert atmosphere. Temperatures must be kept low to minimise formation of peroxides and other products. Moisture may cause mst-initiated polymerization. 

Formates. lron(Il) formate dihydrate [13266-734], Fe(HC02)2 2H20, is a green salt which can be prepared from iron(Il) sulfate and sodium formate in an inert atmosphere. The compound is slightly soluble in water and fairly resistant to air oxidation. The anhydrous salt [3047-594] is known. 

Acetates. Anhydrous iron(II) acetate [3094-87-9J, Ee(C2H202)2, can be prepared by dissolving iron scraps or turnings in anhydrous acetic acid ( 2% acetic anhydride) under an inert atmosphere. It is a colorless compound that can be recrystaUized from water to afford hydrated species. Iron(II) acetate is used in the preparation of dark shades of inks (qv) and dyes and is used as a mordant in dyeing (see Dyes and dye intermediates). An iron acetate salt [2140-52-5] that is a mixture of indefinite proportions of iron(II) and iron(III) can be obtained by concentration of the black Hquors obtained by dissolution of scrap iron in acetic acid. It is used as a catalyst of acetylation and carbonylation reactions. 

Eor some uses, higher molecular weight polymer consisting of 150—200 repeat units is required. Such polymer usually is prepared by soHd-state polymerization in which pellets are heated under an inert atmosphere to 200—240°C. The 2G is removed continuously. The rate of polymerization depends on particle size, end group composition, and crystallinity (65). 

The Type T thermocouple (Table 11.63) is popular for the temperature region below 0°C (but see under Type E). It can be used in vacuum, or in oxidizing, reducing, or inert atmospheres. 

---