Ground glass joints

Ground-glass Joints.—Apparatus provided with ground-glass joints for attachment to other pieces are available for most of the common operations and should be employed for the sake of convenience and of avoiding the introduction of impurities from corks. 

The solid product obtained from a chemical reaction is seldom pure, being contaminated with various impurities and by-products. For 

---

It is often advisable to lubricate ground-glass joint surfaces with an extremely thin film of vaseline. This applies particularly to joints employed in assemblies for distillation under reduced pressure. For distillations under greatly reduced pressures or at very high temperatures it is essential to employ a special lubricant, e.g., silicone grease. 

Although apparatus employing ground-glass joints is excellent for work on a macro scale, it is not always suitable for very small-scale work as the joints are often disproportionately large compared with the rest of the assembly. The semi-micro apparatus described on pp. 59-72 can therefore be considered as being of general utility for this scale of work, especially as the use of corks has been reduced to a minimum. 

In most of these prcpiirations. the corks or rubber-bungs can be replaced by ground-glass joints (pp. 42-47). 

Fit two similar 250 ml. conical flasks, A and B, with reflux water-condensers (using ground-glass joints or rubber stoppers) and connect the condensers in series as before over two water-baths. Prepare a mixture of 2 volumes of acetic anhydride and i volume of glacial acetic acid,... 

Apparatus. The apparatus is made of Pyrex glass, in one piece. It consists of a shaped bulb A (Fig. 89 of about 30 ml. capacity in which the reaction takes place, provided with an inclined inlet B at the side and a vertical ascension tube D. B serves not only as an inlet for the admission of the carrier gas but also as the route by which the reagents and test sample are introduced into the apparatus. B ends in a small ground-glass joint into which fits ajoint carrying a capillary-tube which projects well down into the bulb A (the end of the capillary should be just above the liquid level when the apparatus is charged for the determination). The upper extension of this capillary beyond the joint is provided with a tap C to control the rate of flow of the carrier gas. 

Some simple apparatus, suitable for high vacuum distillation, are collected in Figs. 11, 26, 1-4. Fig. 11, 26, 1 represents an apparatus, which is particularly well adapted for solids the ground glass joint must be lubricated with a grease of negligible vapour pressure. Hickman s vacuum still is shown in Fig. 11, 26, 2 it is about 60 mm. in diameter. 

II, 36, 1 is almost self explanatory two ground glass joints are used, but these may be replaced by rubber stoppers, if desired. The crude substance is placed in the flask A. Stopcocks 1 and 2 are closed, and the apparatus is exhausted through tap 3 the indifferent gas is then allowed to enter the apparatus to atmospheric pressure. The evacuation and filling with inert gas are repeated several times. The solvent is added through the tap funnel B. 

Higher alcohols. These may be purified by drying with anhydrous potassium carbonate or with anhydrous calcium sulphate, and fractionated after filtration from the desiccant. Bark corks (or ground glass joints) should be used rubber stoppers are slightly attacked. The boiUng points of the fractions to be collected are as follows —... 

APPARATUS WITH INTERCHANGEABLE GROUND GLASS JOINTS... 

Dimensions of British Standard Interchangeable Ground Glass Joints... 

Table II, 54.2. Dimensions of U.S.A. Standabd Interchangeable Ground Glass Joints...

AU ground glass joints should be constructed of a high resistance glass, such as Pyrex. The most common form is shown in Fig. II, 55, 1, and this is the type largely encountered in practice. Fig. II, 55, 2 is... 

APPARATUS WITH INTERCHANGEABLE GROUND GLASS JOINTS SUITABLE FOR GENERAL USE IN PREPARATIVE ORGANIC CHEMISTRY... 

Receiver adapters or connectors. Various forms of receiver adapters are shown in Figs. 11, 56, 26-29. The simplest form. Fig. 11, 56, 26, carries a glass hook for securing it to the condenser by means of a rubber band from the side tube to the hook an improved form, incorporating two ground glass joints is shown in Fig. 11, 56, 27. A useful adapter is illustrated in Fig. 11, 56, 28 when employed at atmospheric pressure, a drying tube may be attached to the side tube, if desired in a distillation under reduced pressure, the side tube is connected to the pump. Fig. 11, 56, 29 depicts a receiver adapter with an additional socket connection. 

Solids by solvents. The various forms of Soxhlet apparatus illus trated in Section 11,44 can be purchased with ground glass joints. A simplified form, in which the fragile side tubes are absent, is shown in Fig. II, 58, 1. The material to be extracted, if of granular form, may rest upon a sintered glass disc or upon a removable septum ... 

Sticking of ground glass joints. Provided adequate care is... 

It is hoped that the account of the interchangeable ground glass joint apparatus already given will serve as an introduction to the subject. For the numerous apphcations of such apparatus, the reader is referred... 

Some typical assembhes are collected in the following diagrams. In all cases where thermometers with ground glass joints are shown, thej may be replaced by rubber stoppers, as fully detailed in the description of Fig. II, 56, 6. 

Owing to the corrosive action of bromine upon corks j-jg 7, l. and rubber stoppers, ground glass joints are recommended in this preparation. The apparatus, depicted in Fig. Ill, 37, 1, is particularly convenient for the preparation of bromides from alcohols. A double surface condenser is fitted into D and a round-bottomed flask is fitted on to the ground glass joint at C R is a three-way stopcock f which permits the removal of the contents of A without disconnecting the apparatus. For preparations of moderate size, A has a capacity of 60 or 100 ml. and a 250 or 500 ml. flask is attached at C. 

I) The flask should preferably be connected to the condenser by means of a ground glass joint if not available, an old rubber stopper may be used. 

Ketonic hydrolysis to di-iso-propyl ketone. Mix 15 g. of the ester with 30 ml. of glacial acetic acid, 10 ml. of water and 10 ml. of concentrated sulphuric acid, and reflux in a flask coimected by a ground glass joint... 

Old rubber stoppers may be used, but are slifthtly attacked. Asbestos-sodium silicate Stoppers (for preparation, see Section III,161,Note 2) or ground glass joints are, of course, to be preferred. 

Ideal connections for chlorine are ground glass joints, but previously used and well-fitting rubber stoppers give satisfactory results. Owing to the poisonous character of chlorine, the apparatus should be fitted up in the fume cupboard. 

---