Water pressure, vacuum

The high-pressure water supply service is employed for the operation of the ordinary filter pump, which finds so many applications in the laboratory. A typical all metal filter pump is illustrated in Fig. 11, 21, 1. It is an advantage to have a non-return valve fitted in the side arm to prevent sucking back if the water is turned off or if the water pressure is suddenly reduced. Theoretically, an efficient filter pump should reduce the pressure in a system to a value equal to the vapour pressure of the water at the temperature of the water of the supply mains. In practice this pressure is rarely attained (it is usually 4 10 mm. higher) because of the leakage of air into the apparatus and the higher temperature of the laboratory. The vapour pressures of water at 5°, 10°, 15°, 20° and 25° are respectively 6-5, 9-2,12-8, 17 5 and 23 8 mm. respectively. It is evident that the vacuum obtained with a water pump will vary considerably with the temperature of the water and therefore with the season of the year in any case a really good vacuum cannot be produced by a filter pump. 

The yellow solution was poured into 150 ml of water. After addition of 20 g of ammonium chloride and vigorous shaking, the layers were separated. The aqueous layer was extracted twice with diethyl ether. The combined solutions were dried over magnesium sulfate and concentrated in a water-pump vacuum. The residue was distilled at low pressure giving the desired carbinol, (b.p. 40°C/0.1 mmHg), n 1.5505 in 66-702 yield. A small viscous residue remained in the distillation flask. 

To a solution of 0.25 mol of the trimethylsilyl ether in 120 ml of dry diethyl ether was added in 20 min at -35°C 0.50 mol of ethyllithium in about 400 ml of diethyl ether (see Chapter II, Exp. 1). After an additional 30 min at -30°C the reaction mixture was poured into a solution of 40 g of ammonium chloride in 300 ml of water. After shaking, the upper layer was separated off and dried over magnesium sulfate and the aqueous layer was extracted twice with diethyl ether. The ethereal solution of the cumulenic ether was concentrated in a water-pump vacuum and the residue carefully distilled through a 30-cm Vigreux column at 1 mmHg. The product passed over at about 55°C, had 1.5118, and was obtained in a yield of 874. Distillation at water-pump pressure (b.p. 72°C/I5 mmHg) gave some losses due to polymerization. 

The combined ethereal solutions were washed with water and dried over magnesium sulfate. The greater part of the diethyl ether was distilled off at normal pressure through a 40-cm Vigreux column, keeping the bath temperature below 65°C (note 2), (see Fig. 5). The distillation flask was then cooled to 20-30°C and the remaining diethyl ether was removed in a water-pump vacuum, keeping the receiver immersed... 

Lithium Iodide. Lithium iodide [10377-51 -2/, Lil, is the most difficult lithium halide to prepare and has few appHcations. Aqueous solutions of the salt can be prepared by carehil neutralization of hydroiodic acid with lithium carbonate or lithium hydroxide. Concentration of the aqueous solution leads successively to the trihydrate [7790-22-9] dihydrate [17023-25-5] and monohydrate [17023-24 ] which melt congmendy at 75, 79, and 130°C, respectively. The anhydrous salt can be obtained by carehil removal of water under vacuum, but because of the strong tendency to oxidize and eliminate iodine which occurs on heating the salt ia air, it is often prepared from reactions of lithium metal or lithium hydride with iodine ia organic solvents. The salt is extremely soluble ia water (62.6 wt % at 25°C) (59) and the solutions have extremely low vapor pressures (60). Lithium iodide is used as an electrolyte ia selected lithium battery appHcations, where it is formed in situ from reaction of lithium metal with iodine. It can also be a component of low melting molten salts and as a catalyst ia aldol condensations. 

Vacuum Relief and Combined Pressure-Vacuum Relief for Low Pressure Conditions normally used for low pressures such as 1 ounce water to 1.5 psig above atmospheric by special spring or dead weight loading and for vacuum protection such as 0.5 psi below atmospheric. Usually these conditions are encountered in large process, crude oil, ammonia, etc., storage tanks. See later section covering this topic. 

A solution of 25.8 g. (0.20 mole) of 4-amino-2,2,4-trimethyl-pentane (ierf-octylamine) (Note 1) in 500 ml. of C.P. acetone is placed in a 1-1. three-necked flask equipped with a Tru-Bore stirrer and a thermometer and is diluted with a solution of 30 g. of magnesium sulfate (Note 2) in 125 ml. of water. Potassium permanganate (190 g., 1.20 moles) is added to the well-stirred reaction mixture in small portions over a period of about 30 minutes (Note 3). During the addition the temperature of the mixture is maintained at 25-30° (Note 4), and the mixture is stirred for an additional 48 hours at this same temperature (Note 5). The reaction mixture is stirred under water-aspirator vacuum at an internal temperature of about 30° until most of the acetone is removed (Note 6). The resulting viscous mixture is steam-distilled approximately 500 ml. of water and a pale-blue organic layer are collected. The distillate is extracted with pentane, the extract is dried over anhydrous sodium sulfate, and the pentane is removed by distillation at atmospheric pressure. The residue is distilled through a column (Note 7) at reduced pressure to give 22-26 g. (69-82%) of colorless 4-nitro-2,2,4-trimethylpentane, b.p. 53-5473 mm., < 1.4314, m.p. 23.5-23.7°. 

Suction lysimeters are required for some field-scale groundwater monitoring studies to monitor the transport of compounds of interest through the unsaturated zone. Unlike monitoring wells or water supply wells that sample water from the saturated zone, suction lysimeters sample water from the unsaturated zone. This section provides a summary of the installation and sampling procedures for pressure-vacuum suction lysimeters. A detailed discussion of unsaturated zone sampling devices is available elsewhere. 

Soilmoisture Equipment Corp., Operating Instructions for the Pressure-Vacuum Soil Water Sampler, Soilmoisture Equipment Corp., Santa Barbara, CA (1997). 

Traces of acid adhering to glassware are sufficient to induce explosive decomposition of the alcohol dining distillation, and must be neutralised by pre-treatment with ammonia gas. Low pressures and temperatures are essential during distillation. Explosions during distillation using water pump vacuum and bath temperatures above 115°C were frequent. 

Large storage tanks are designed to withstand low pressures and vacuums. Typically they are constructed to withstand no more than 8 in of water gauge pressure and 2.5 in of water gauge vacuum. A particular tank is 30 ft in diameter. 

Storage tanks typically are not capable of withstanding much pressure or vacuum. Standard storage tanks are designed for a maximum of 2.5 in of water gauge vacuum (0.1 psi) and about 6 in of water gauge pressure (0.2 psi). 

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