. Practical methods of organic chemistry . ff smoothlywithout splintering. If the glass does not crack at once,the heated portion is moistened with a few drops of /water, and the breaking off will follow with certainty. Volhard Tubes. — The tube described by Volhard(Fig. 46) may be used to great advantage when it isdesired to heat large quantities of substances in a singletube. It consists of a wide tube to the end of which anarrower one is fused. A tube of this kind, 35 mm. indiameter and 45 cm. in length, contains about \ of alitre, and possesses the further advantage of being easyto seal. I
. Practical methods of organic chemistry . ff smoothlywithout splintering. If the glass does not crack at once,the heated portion is moistened with a few drops of /water, and the breaking off will follow with certainty. Volhard Tubes. — The tube described by Volhard(Fig. 46) may be used to great advantage when it isdesired to heat large quantities of substances in a singletube. It consists of a wide tube to the end of which anarrower one is fused. A tube of this kind, 35 mm. indiameter and 45 cm. in length, contains about \ of alitre, and possesses the further advantage of being easyto seal. If on opening the tube care be taken, to cutoff as small a portion of the narrow end as possible,it may be used repeatedly. If, finally, the narrowedportion becomes too short, another piece of the samekind of tubing is sealed on. - ig. 4 . Pressure Flasks. Autoclaves. — In order to heat substancesunder pressure at a moderate temperature which on reacting witheach other evolve no gaseous products, so that no pressure due 64 GENERAL PART. to the reaction is developed, they are sometimes enclosed in strong-walled flasks (pressure flasks), wrapped up in a cloth andheated in a water-bath. Very well adapted to this purpose are the commonsoda-water or beer bottles, of the kind representedin Fig. 47. In using them they are not immersed inwater already heated, but are slowly heated with thewater. The water-bath is closed by a loosely fittingcover, so that in case the bottle bursts, one may notbe burned by the hot water. The flasks are notopened until after they arecompletely 47 Large quantities of sub- stances which do not act on metals may be heated under pressure in closed ves-sels, generally made of iron, bronze or copper (autoclaves). Such vessels are not suited for heating acid substances, but may be used for neutral or alkaline substances. In this laboratory Mannes- mann tubes (without seams) are in use, one end being welded together, and the v other is supplied with a
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