Rubber tapping

The air may be collected directly into a Hempel gas-burette (Fig. 76) and there measured. This burette consists of a glass tube H calibrated in ml. from the tap E downwards, and connected by a piece of rubber tubing to the reservoir R, the height of which can be adjusted. The tap E is a 3-way tap. by which the tube H can be connected directly through to the capillary tube above, or either tube can be connected through the left- hand end of the tap to the atmosphere. 

The Mariotte bottle. l he perchlorate guard tube is attached by a length of ordinary rubber condenser tubing to the Mariotte bottle W. This is, in effect, a siphon bottle, and the lead-in tube X is a capillary provided with a tap T,. The bent capillaiy (drawn off slightly at the end) serves as exit tube it is fitted into W by a rubber bung and its level may be adjusted. 

The absorption tubes are then detached from each other, transferred to their stand, and polished, matured and weighed exactly as at the beginning of the experiment, taking care that no particles of rubber or wax are left in the side-arms. They must be repolished, matured and reweighed before they are used for a further determination. Finally when the tube is cool, the tap Tj of the purification train may be closed and the oxygen supply shut off. 

Z-tube. The tube B is made of capillary tubing (3 mm. internal bore) bent into the shape of a Z. It is attached by a length (5 cm.) of very tight-fitting rubber pressure tubing to the tap T, a gla -to-glass join being made inside... 

This tube is connected %vith rubber tubing of about 6 mm. bore to the carbon dioxide Kipp, via a wash-bottle containing sodium carbonate solution (to remove any dilute hydrochloric acid spray). It is very important, when the apparatus is in use, that there should be no constriction or bend in the rubber tube between the tap C and the wash-bottle. If these precautions are taken, a slow, e en, and easily controlled flow of gas can be obtained. 

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. 

Natural Rubber. To obtain natural mbber (NR), the Hevea hrasiliensis tree is tapped for its sap. The off-white sap is collected and coagulated. This process produces a high molecular weight substance which is natural mbber. The principal producing countries are Malaysia, Indonesia, Thailand, India, China, and Sri Lanka (see Rubber, natural). 

An alternative source of the frani-1,4-polyisoprene is balata, obtained from Mimosups balata, occurring in Venezuela, Barbados and Guyana. The latex is thin and may be tapped in the same way as natural rubber. 

Natural rubber is harvested as latex by tapping trees in a manner similar to maple syrup. Tree latex contains about 35 wt% rubber solids, as well as small quantities of carbohydrates, resins, mineral salts and fatty acids. Ammonia should be immediately added to the latex to avoid coagulation by these other ingredients and to prevent bacterial degradation. After collection, the latex can be concentrated to 60-70% solids if the latex product is required for end-use. Otherwise, the latex is coagulated, washed, dried, and pressed into bales for use as dry rubber. 

Total Ionic Strength Adjustment Buffer (TISAB). Dissolve 57 mL acetic acid, 58 g sodium chloride and 4g cyclohexane diaminotetra-acetic acid (CDTA) in 500 mL of de-ionised water contained in a large beaker. Stand the beaker inside a water bath fitted with a constant-level device, and place a rubber tube connected to the cold water tap inside the bath. Allow water to flow slowly into the bath and discharge through the constant level this will ensure that in the... 

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