Phosphorus pentoxide technique

The gravimetric method is accepted as the most accurate humidity-measuring technique. In this method a known quantity of gas is passed over a moisture-absorbing chemical such as phosphorus pentoxide, and the increase in weight is determined. It is mainly used for calibrating standards and measurements of gases with SO, present. 

Manganese(II) thiocyanate (0.05 mole, 8.55 g) is dissolved in 100 mL of water. Then 1,2,4-triazole (0.1 mole 6.91 g), dissolved in 50 mL of water, is added. A few drops of concentrated nitric acid are added and the solution is heated to boiling, cooled immediately to room temperature and stored for several days in a desiccator above phosphorus pentoxide. The yield of the product, recovered by Filtration, washed with water and dried under vacuum is —12 g or about 75%. The crystals have the shape of flat rhombi, almost squares, with a thickness of about one-fifth of the largest diameter. Crystal diameters may vary from 1-10 mm depending upon the preparative technique. Crystallization of this compound occurs more slowly than for the compounds containing other metals. 

General. Pyridine is distilled from p-toluenesulfonyl chloride and then from calcium hydride and stored over potassium hydroxide. N,N-Di-methylformamide is distilled from calcium hydride and stored over molecular sieves. Dioxane is distilled from phosphorus pentoxide. Tri-n-butylamine, triethylamine, diphenyl phosphorochloridate, and o- and p-fluorobenzoyl chlorides are distilled before use. Tri-n-butylammonium pyrophosphate is prepared at room temperature according to the method of Moffatt and Khorana and stored at 5°. Paper chromatography is carried out by the descending technique on Whatman No. 1 paper in (A) isobutyric acid-1 M NH4OH (60 40) and (B) 1-propanol-water (7 3). Electrophoresis is carried out on Whatman No. 1 paper at pH 3.5 in 0.035 M citric acid-0.0148 M sodium citrate (1 1). Evaporations are carried out under reduced pressure at bath temperatures below 30°. Phosphate analyses of nucleoside triphosphates are performed by the method of Lowry and Lopez after treatment of approximately 1 / mole of these compounds for 60 min at 22° in 1 ml of Tris chloride at pH 10.4 containing 0.02 mg of alkaline phosphatase of calf intestinal mucosa (type VII, Sigma Chemical Co.). 

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