Toepler pumps

Mass spectral, gas chromatographic, and Toepler pump analyses of the gases above irradiated benzene solutions show the formation of with an average of 1.9 mole of released per... 

Hydrogen Analysis. The thermal decomposition technique was used to determine the hydrogen elemental composition. The sample was heated in vacuo to 925°C and was maintained at that temperature until all evolved gas was transferred by way of a Toepler pump to a calibrated gas buret. 

Experiments were terminated by expanding the contents of the 155 °C. reaction vessel into the analytical side of the vacuum line, which contained a detachable GLPC sampling bulb in parallel with two liquid nitrogen traps and in series with a Toepler pump, gas buret, and Cu-CuO furnace. The noncondensable gases were estimated as described above. Corrections were applied for that portion of the reaction mixture diverted to the GLPC sampling bulb. 

Fig. 5.9. Toepler pump and gas buret. In this installation a constant-volume" manometer is used for measuring the pressure. Stopcock B allows the attachment of a sampling bulb or a large expansion bulb for use with large volumes of gas. Stopcock A is used for initial evacuation of the calibrated volume and sample bulbs. It is closed during the operation of the pump. When a gas is to be measured, the mercury levels in the right arm of the Toepler pump and in the left arm of the manometer are adjusted to levels (C) for which the gas volume has been calibrated. An excellent version of this pump is manufactured by the Rodder Instrument Co., Los Altos, Calif.

This chapter is primarily devoted to pumps for high vacuum-operation (10 3-10 5 torr), which is the vacuum range of greatest interest in chemical vacuum lines. In addition, rough-vacuum systems (760-0.1 torr) are discussed in connection with their use in manipulating mercury-filled apparatus, such as Toepler pumps and McLeod gauges. 

After hydrolysis or similar reaction, the tube is cooled in liquid nitrogen to reduce the pressure of the gases and opened with a special device (Fig. 9.32). If noncondensable gases result, they are collected with the Toepler pump or low temperature adsorption for measurement and identification. 

A. Toepler Pump. The principles of operation of a Toepler pump are outlined in Fig. 5.9, where it will be noted that a system of internal check valves permits gas from the vacuum system to enter the upper chamber, and subsequently to be compressed and expelled into a gas buret. The system may be man-... 

Fig. 6.1. Rough-vacuum system. Frequently used items such as the Toepler pump and constant-volume manometer are often connected permanently into the rough-vacuum system. Also, one or two outlets, with vacuum tubing attached, are included for general use. The manifold generally is constructed from rigid plastic or metal tubing.

F. Cleaning Mercury. When it is received, mercury is generally covered with a scum which can foul manometers, Toepler pumps, and similar apparatus. This scum can be removed by a simple filtration procedure. A standard filter paper is folded to fit an appropriate funnel and a pinhole is pierced in the tip. The hole must be large enough so that mercury droplets will run through, but small enough so that the last drop and its associated scum are retained by its surface tension. This type of filtration process is routinely performed before filling an apparatus. 

In 1851, Newman developed a mechanical pump that achieved a vacuum of 30.06 in. of mercury on a day that the barometer was reading 30.08 in. This pump was very impressive for the time. Vacuum technology was further enhanced by the invention of the Toepler pump in 1862, the Sprengel pump in 1865, and the McLeod gauge in 1874. 

Fig. 7.27 General layout of a typical electrically operated Toepler pump.

Toepler pumps are used for the collection and transfer of noncondensable gases. They are not capable of creating great vacuums, but they can be very effective pumps regardless. A 500-cm3-size Toepler pump can remove 99.9% of a two-liter gas bulb in 10 minutes. 

A Toepler pump is a piston pump with mercury as the piston. The mercury piston is powered by both the vacuum from a vacuum system and the atmosphere. The actual operation of a Toepler pump involves evacuation followed by readmission of air out of, and into, the Toepler pump. There have been a wide variety of techniques to automate this process because manual operation can be quite tedious. 

Fig. 7.28 By placing a Toepler pump (or any mercury-containing device) in a plastic container, spills are avoided and it s protected from an accidental bump.

As with most items on a vacuum line that contain mercury, place the Toepler pump in a secondary container that is firmly attached to another surface to contain any mercury that may spill from an accident as well as protect the pump from accidental bumps (see Fig. 7.28). Plastic containers (such as plastic milk cartons) are particularly good because the mercury will not affect plastic. Conversely, mercury may amalgamate with the metals in a metal can, which could destroy any containment capabilities. In addition, it is easier to get mercury out of a plastic container (with smooth walls) than out of a metal one (with a narrow rim). The plastic tub can be glued onto the table with some epoxy. The epoxy will stick better if you roughen up the bottom surface of the plastic container with sandpaper. Because not all epoxies stick to plastic, test the epoxy before assuming that it will hold. 

The methyllithium is obtained as a 5% solution in diethyl ether. It is stored in a refrigerator at —20° until ready for use. The solution is standardized by measuring the amount of methane gas evolved when a sample is added to methanol. The gas analyses are carried out by hydrolyzing the sample on a standard vacuum line equipped with a Toepler pump.3... 

Analysis is accomplished by standard vacuum-line techniques. A 1.00-mL aliquot of (CH3)3N-A1H3 in benzene solution is placed in an ampul and attached to a multipurpose vacuum line equipped with gas-separation traps and a Toepler pump and is hydrolyzed by using a mixture composed of equal amounts of water and concentrated hydrochloric acid. 

In this case a Toepler pump can be used to remove the volatile products derived from a known mass of the gallane, and an efficient trap cooled to 77 K to separate the condensable B2H6 from the noncondensable H2 the two fractions are then assayed tensimetrically. The mass balance is completed simply by weighing the residue of elemental gallium. Similar measures can be adopted to determine the stoicheiometry of a reaction engaging a gallane with another compound, e.g., NH3, NMe3, or HC1. 

---