PART II. PREPARATION XLIII. ETHYL BROMIDE, CH, Br. LITERATURE-Serullas (1827), Ann. Ch. Phys. 34, 99; Personne (1861), Compt. rend. 52, 468. 10 grms. amorphous phosphorus. 10 grms., amorphous phosphorus are placed in a dry round-bottomed flask of about litre capacity, connected with condenser and receiver, together with 60 grms. commercial absolute alcohol; 60 grms. bromine are slowly run in from a tap funnel, the flask being cooled if necessary during the operation. After standing for a few hours the mixture is distilled on the water-bath, the temperature of which is slowly raised (Fig. 20). The reddish distillate, consisting of ethyl bromide and alcohol, is shaken with double the volume of water to which soda solution is added until slightly alkaline. The ethyl bromide, which sinks to the bottom of the vessel, is drawn off by a tap funnel, and is then shaken repeatedly with water. It is separ ated as completely as possible from water and dehydrated over pieces of fused calcium chloride. The FIG. 20. clear liquid after being decanted is distilled on the water-bath, a thermometer being inserted through the cork of the distilling flask. The ethyl bromide distils at 36-40° and may be further purified by a second distillation. 5C2H5(OH) + 5Br + P = 5C,H,Br+ H2PО + H2O Properties.-Colourless liquid; b. p. 38.8°; sp. gr. 1°47 at 13 ̊5°. Determination of Specific Gravity.-A simple method for determining the specific gravity of liquids is as follows: A small glass bottle of about 20-30 c.c. capacity, which can be readily made by the help of the blow-pipe (Fig. 21), is fitted with a cork. The neck of the vessel just above the bulb is narrowed by drawing it out in the flame, and a horizontal mark m etched or scratched on it with a file. The bottle is thoroughly cleaned, dried in the air-bath, allowed to cool and weighed. It is then filled with the liquid, which is poured in through a funnel, the stem of which is drawn out so as to pass through the constricted neck. The bottle is placed in a mixture of snow or pounded ice and a little water and left to tents have a temperature of o°. hour until the conThe meniscus is now H adjusted until it coincides with the mark on the neck of the bottle. If more liquid has to be added this may be done from a small pipette with capillary delivery tube; if some of the liquid has to be removed a piece of bibulous paper may be used to absorb it. The bottle is then corked, dried, allowed to remain hour in the balance case and weighed. It is then emptied, cleaned and dried and filled with distilled water previously boiled. The water is cooled to o°, the meniscus adjusted and the bottle weighed, the same process being repeated as that just described. The following expression will give the specific gravity of the liquid at oo compared with water at 4° and reduced to a vacuum. W3 = = p = σ = apparent weight of the empty bottle. at oo apparent weight of the bottle and liquid at o° density of water at oo --- *999873. density of air at t° (temperature of the balance room). A very delicate and useful piece of apparatus, which is readily made with the blow-pipe, is Perkin's modification of Sprengel's specific gravity tube (Chem. Soc. J. 45, 421). It is especially adapted for small quantities of liquid and for the more volatile ones. The apparatus (Fig. 22) consists of a U-tube to hold from 2 to 10 c.c., drawn out at each end into a fine capillary. The one capillary limb (a) is bent a FIG. 22. outwards and is furnished with a small bulb, the other (b) is bent at a right angle with the first. On the limb a, between the bulb and the top of the U-tube, a mark is scratched. The tube is dried and weighed, and the liquid drawn in through the limb b until it half fills the small bulb on the limb a. The apparatus |