NITROGEN DIOXIDE.181 SODIUM HYDROXIDE

Nitrogen. To one portion of the filtrate, add z-3 ml. of 10, aqueous sodium hydroxide solution, then add about o-2 g. of ferrous sulphate and proceed as in the Lassaigiie nitrogen test (p, 322). Note, however, that the fiUal acidification with dilute siiphiiric acid must be made with care, owing to the vigorous evolution of carbon dioxide from the carbonate present. 

Nitrogen. Treat one portion with 1-2 ml. of 5 per cent, sodium hydroxide solution and 0 1 g. of powdered ferrous sidphate. Boil for 1 minute and cool. Cautiously acidify with dilute sulphuric acid (carbon dioxide is evolved). A precipitate of Prussian blue indicates that nitrogen is present. 

If the pump is a filter pump off a high-pressure water supply, its performance will be limited by the temperature of the water because the vapour pressure of water at 10°, 15°, 20° and 25° is 9.2, 12.8, 17.5 and 23.8 mm Hg respectively. The pressure can be measured with an ordinary manometer. For vacuums in the range lO" mm Hg to 10 mm Hg, rotary mechanical pumps (oil pumps) are used and the pressure can be measured with a Vacustat McLeod type gauge. If still higher vacuums are required, for example for high vacuum sublimations, a mercury diffusion pump is suitable. Such a pump can provide a vacuum up to 10" mm Hg. For better efficiencies, the pump can be backed up by a mechanical pump. In all cases, the mercury pump is connected to the distillation apparatus through several traps to remove mercury vapours. These traps may operate by chemical action, for example the use of sodium hydroxide pellets to react with acids, or by condensation, in which case empty tubes cooled in solid carbon dioxide-ethanol or liquid nitrogen (contained in wide-mouthed Dewar flasks) are used. 

Lead hydroxide Litliimn amide Methyl ethyl pyridine Sodamide Sodium cyanide Nitrogen dioxide Nitric acid... 

AMMONIUM CHLORIDE NITRIC OXIDE NITROGEN DIOXIDE HYDRAZINE NITROUS OXIDE SODIUM CYANIDE SODIUM FLUORIDE SODIUM HYDROXIDE NICKEL... 

In all cases, the pump is connected to the still through several traps to remove vapours. These traps may operate by chemical action, for example the use of sodium hydroxide pellets to react with acids, or by condensation, in which case empty tubes cooled in solid carbon dioxide-ethanol or liquid nitrogen (contained in wide-mouthed Dewar flasks) are used. 

After about 3 hours or after analysis has indicated that the peroxide has been consumed (Note 5), the formic acid is removed by distillation under reduced pressure (b.p. 50°/125 mm.) in a stream of gas (carbon dioxide or nitrogen) to prevent bumping (Note 6). The residue in the flask, which consists of hydroxy-formoxystearic acids, is heated for 1 hour at 100° with an excess of 3N aqueous sodium hydroxide, and the hot, amber-colored soap solution is cautiously poured into an excess of 3N hydrochloric acid with stirring. The oil which separates is allowed to solidify, and the aqueous layer is discarded. The tan-colored solid is remelted on the steam bath by addition of hot water and stirred well to remove residual salts and water-soluble acids (Note 7). When the oil has solidified, the aqueous layer is discarded, and the solid is broken into small pieces and dissolved in 400 ml. of 95% ethanol by heating on the steam bath. After crystallization at 0° for several hours, the product is collected on a filter and dried under vacuum. The yield of crude 9,10-dihy-droxystearic acid is 75-80 g., m.p. 85-90°. After a second recrystallization from 250 ml. of 95% ethanol, the product weighs about 60-65 g. and melts at about 90-92°. A third recrystallization may be necessary to produce a pure product melting at 94-95°. The over-all yield is 55-60 g. (50-55%, based on the available oleic acid) (Note 8). 

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