Sealing ground joints

In most cases the problem of ensuring that ground joints and taps are leak-proof needs attention. The substances to be distilled have widely different solvent powers for joint greases, so that preliminary tests may be necessary to find the most suitable lubricant. Some data on the subject are given in Table 79. 

The experience obtained with silicone greases is not yet sufficient to allow a definite judgment. There is some danger that components of the grease will enter the column and affect the wetting of the packing, and it is difficult to remove the white, powdery filler which remains when the silicone itself has been leached out. 

Type of grease Maximum operating temp. ( C) Composition or manufacturer Application 

Ramsay grease 25 6 pts. vaseline 1 pt. paraffin wax 6 pts. Para rubber General work 

High vacuum jpoase P 25 E. Leybold s Nachf., Cologne, High-vacuum work 

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The swan neck adapter of Fig. II, 56, 12 is useful for distillations as it permits the use of a capillary tube (held in position by a short length of heavy-walled rubber tubing) not sealed to a ground joint. It may also be used for inser tion of a thermometer or a gas-inlet tube in the narrow neck and a reflux condenser into the ground joint this device virtually converts a three-necked into a four-necked flask. Common sizes are cone fil9, 24, 29, or 34 socket 19, 24 or 29. 

Teflon sleeves are used to assure the vacuum tight connection between the ground joints subjected to heat. The checkers used clear-seal joints in all of the glass connections. 

A 500-cc. three-necked flask, equipped with ground joints, is fitted with a mercury-sealed stirrer (Note 1), a reflux condenser,... 

Figure 26.8 (A) Suction equipment for TLC. (B) Equipment for polarography of small volumes 1, upper part of ground joint 2, mantle of the ground joint 3, electrolysis cell 4, water container sealing the inner space. [From Ref. 84.]...

Ground joint stoppers and snap-on plastic caps are commonplace, but many laboratory containers do not come with built in stoppers or seals. In the absence of a formal closure, or closures such as corks or rubber stoppers, there is the covering film, PARAFILM M . ... 

The desiccator lid was manufactured with a ring stopcock through which evacuation was accomplished. A center tube was sealed on the lid, connecting it to a bulb. The bulb contained the saturated salt solution that maintained a constant water vapor pressure over the specimens. The bulb was isolable by means of a stopcock, so that the saturated salt solution could be stored under vacuum while samples were being changed. A ground joint connection made it possible to remove the whole upper assembly from the lid. Six such desiccators were employed, a different water vapor pressure being maintained in each. The relative... 

The chlorination apparatus, Fig. 1, consists of a 24-mm od quartz tube with a ground joint socket joined by way of a quartz-pyrex seal to a collection flask. For metal quantities of about 20 g a 250-mL flask should be used and for 5-g quantities a 100-mL flask is convenient. 

A tube (20 cm. long and 2 cm. in diameter) with a porous disk (porosity 3 or medium) sealed in at one end and with an ungreased ground joint, is arranged as shown in Fig. 8. Rhodium(III) chloride 3-hydrate (11.0 g. 0.042 mol) is pulverized and placed on top of the disk. The apparatus... 

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