Manostats

The maintenance of a constant pressure in a system during distillation under diminished pressure is of great practical importance if trustworthy boiling points are desired. Devices which maintain a constant pressure in a system that is higher than the minimum pressure that the pump will give are termed manostats. A simple manostat, due to M. S. Newman, is illustrated in Fig. II, 23, 4. 

An excellent manostat, based on the Cartesian diver principle, is marketed under the name of Cartesian manostat. 

The action of the manostat may be explained with the aid of Fig. II, 23, 6. Mercury is introduced into the container until the disc of the float just makes contact with the oriflce, when the pressure is equalised inside and outside the float. The device is connected to the pump and to the system by way of a large reservoir and a manometer. With the stopcock open, the pressure in the system is reduced by way of a by-pass between the pump and the system until the desired value as read on the manometer is reached, then both the stopcock and by-pass are... 

The commercial form of Cartesian manostat, model 7A, is depicted in Fig. II, 23, 7 it is normally charged with mercury except for very low pressures when di-w-butyl phthalate is employed. The manostat is highly sensitive in its action furthermore, once the pressure has been set in the instrument, the system may be shut down without disturbing the setting. 

Supplied by The Emil Greiner Co. of New York and by Edwards High Vacuum Ltd. an all.metal Cartesian manostat is also marketed. 

This pressure is readily attained by placing an air leak between the water pump and the apparatus or, better, with the aid of a manostat. Figs. II, 23, 4-7. 

The operating steps are very similar as for a gas exchange, except that a defined partial pressure is maintained during the whole experiment. Care must be taken that any gaseous reaction products generated do not change the pressure set. If necessary the pressure must be controlled and kept constant by means of a manostat. 

For the final distillation the pressure is regulated by means of a manostat. 

A 1-L, three-neck flask was fitted with dropping funnel, a small spinning-band column and a thermometer. Into it were placed a 40% dispersion of Na in mineral oil (38 g, 0.66 mol) and Irielhylene glycol dimethyl ether (375 mL) (freshly vacuum distilled from Na). The flask was heated in an oil bath to 120 CC and a manostat maintained the pressure at 80 Torr. A dry ice chilled trap was present in the line. Over 30 min, a solution of 2,2,4,4-tetramethyl-J,3-dichlorocyclobutanc (69 32 g, 176 mmol) in triethylene glycol dimethyl ether (50 mL) was added at a rate which maintained the internal temperature at 130-140 C. The reaction was moderately exothermic and the mixture turned bright blue. The product was distilled at... 

Logarithmic plots of the Freundlich equation, Q = kpn, where Q is the amount of methane adsorbed at a pressure p, and k and n are constants, for methane adsorption at 0°, 30° and 50°C. in Figures 6 and 7 indicate that the equation is valid up to at least 1000 torr. Equilibrium sorption points obtained on different samples in a manostatic adsorption apparatus are shown as solid points in Figures 6 and 7. The exponent n varied from 0.72 at 0° to 0.87 at 50°C. for the Pocahontas coal and from 0.78 at 0° to 0.94 at 50°C. for Pittsburgh coal (Table III). 

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