Hempel

M, J P Bielawski, J C Hempel and M Waldman 1996. Optimisation and Visualisation of ecular Diversity of Combinatorial Libraries. Molecular Diversity 2 64-74. 

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. 

A modified Hempel column, which incorporates a small reflux condenser ( cold finger or cold spot condenser ), is shown in Fig. 11,... 

Fig. II, 16, 1 illustrates a set-up for simple fractionation a Hempel column is shown, but it may be substituted by a modified Hempel, a Vigreux or an all-glass Dufiton column. The Hempel column may be filled with glass rings, h porcelain Lessing rings, or with porcelain rings. The mixture to be fractionated is placed in a bolt - head flask of convenient size (it should be one third to one half full), a few fragments of porous porcelain added, the column fixed in position, and a water condenserattacfied to the side arm. The distillate is collected in small flasks or in test tubes. The bulb of the thermometer should be just below the level of the side arm.

The 40-45 per cent, hydrazine solution may be concentrated as follows. A mixture of 150 g. (144 ml.) of the solution and 230 ml. of xylene is distilled from a 500 ml. round-bottomed flask through a well-lagged Hempel (or other efficient fractionating) column fitted into a cork covered with tin foil. All the xylene passes over with about 85 ml. of water. Upon distillation of the residue, about 50 g. of 90-95 per cent, hydrazine hydrate (5) are obtained. 

Fractional distillation. Fig. II, 60, 2 illustrates a set-up for fractional distillation wdth a Hempel-type column and cold finger, the latter to give manual control of the reflux ratio. Any other fractionating colunm, e.g., an all-glass Dufton or a Widmer column may, of course, be used. 

Alternatively, a modified Hempel column (Fig. 77,15, 5) or an all glass Dufton column with 30 cm. spiral (Fig. 77,15, 2) may be used for the fractionation. The latter has the advantage that it is more easily cleaned. 

Fit up the apparatus shown in Fig. Ill, 61, 1. The bolt-head flask is of 500 ml. capacity and the Hempel column is fllled with glass rings... 

The best results are obtained b distillation from a small flask through a short fractionating column a Hempel column tilled with glass rings (Fig. 11,16, 1) and lagged with asbestos cloth or several thicknesses of linen cloth is quite satisfactory. 

Alternatively, an independent column (Fig. XII, 2, 8, c) may be inserted into a flask the column may be of the Vigreux, Widmer or Hempel form. The fractionating column should be lagged with asbestos cloth or string for distillation temperatures above 100° for the best results the column should be heated electrically (compare Section 11,15) to a temperature 5-10° below the b.p. of the fraction being collected. The side arm of the flask or fractionating column may be attached to a cold spot condenser and receiver as in Fig. XII, 2, 4 or to a Liebig s condenser and receiver as in Fig. XII, 2, 1. 

R. E. Davis, "Electrowinning of Cesium and Rubidium," in C. A. Hempel, ed., Emyclopedia of Electrochemistry, Reinhold Publishing Corp., 1964. 

Crotyl bromide [29576-14-5] M 135.0, b 103-105 /740mm, n s 1.4792. Dried with MgS04, CaC03 mixture. Fractionally distd through an all-glass Todd column. [Todd column. A column (which may be a Dufton type, fitted with a Monel metal rod and spiral, or a Hempel type, fitted with glass helices) which is surrounded by an open heating jacket so that the temperature can be adjusted to be close to the distillation temperature (Todd Ind Eng Chem (Anal Ed) 17 175 1945)]. 

Hempel fractionating column, 137 Hofmann s bottles 30 Hot-water funnel, 53 Hydrazobenzene, 146 Hydriodic acid, 113 Hydrobenzamide, 196 Hydrobromic acid, 140 Hydrochloric add gas, 93 Hydrocinnamic acid, 204 Hydrogen, qualitative determination, r quantitative, ... 

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