Stoppers, end

Caution Excess pressure may be generated The rubber stopper must be held tightly and the pressure released by opening the stopcock once or twice. The tube is now fixed vertically to the stand with the stoppered end uppermost. The stopper is removed quickly and the gas mixture ignited with the flame of the gas burner. 

After fusion and cooling, the iron crucibles are opened by sawing off the top and bottom, and the alloy is then punched out of the open cylinder. In another method, the crucible is placed on a lathe, clamped at the stopper end, and its wall turned down to 0.1-0.3 mm. This thin wall can then be stripped off with a pair of pliers in the same manner as the top of a can of sardines. Since this can be done very rapidly, even those alloys which are very sensitive to air can be isolated without too much damage and can be rapidly transferred to a storage vessel filled with a protective gas. The method is also useful in cases where the alloy the crucible walls because of local... 

Compound (7.382) with n 20 is typical of the short-chain linear phosphazenes which have terminal or stopper end groups. Various atoms or groups may act as chain stoppers and many compounds have been isolated which can be represented by the general formula Cl(PNCl2) , where X = PCI3, H, MePOClj, PSCI2 or SOjCl. 

To use the gas laws, you must clearly understand the units used to express pressure, and you must utilize the Kelvin temperature scale introduced in Section 1.6. Pressure is defined as force per unit area. However, most of the units commonly used to express pressure reflect a relationship to barometric measurements of atmospheric pressure. The mercury barometer was invented by Italian physicist Evangelista Torricelli (1608-1647). Its essential components are shown in I Figure 6.5. A glass tube, sealed at one end, is filled with mercury, stoppered, and inverted so the stoppered end is under the surface of a pool of mercury. When the stopper is removed, the mercury in the tube falls until its weight is just balanced by the weight of air pressing on the mercury pool. The pressure of the atmosphere is then expressed in terms of the height of the supported mercury column. 

Meanwhile, the organic compound can be prepared for analysis whilst the sealed end C (Fig. 72) of the Carius tube has been cooling dow n. For this purpose, thoroughly clean and dry a small tube, which is about 6 cm. long and 8-10 mm. w ide. Weigh it carefully, supporting it on the balance pan either by means of a small stand of aluminium foil, or by a short section of a perforated rubber stopper (Fig. 73 (A) and (B) respectively) alternatively the tube may be placed in a small beaker on the balance pan, or suspended above the pan by a small hooked wire girdle. 

The liquid in B rapidly volatilises at the bottom of the tube T, the stopper being thrown off, and bubbles of air escape from D into the tube C. Continue boiling the liquid in J steadily until no more bubbles escape into C. Then carefully slip the end of D from under the tube C, close the end of C securely with the finger, and then transfer the tube to a gas-jar of water, so that the level of the water inside and outside C can be equalised. Measure the volume of air in C, and note the room temperature and the barometric pressure. The vapour density can now be calculated (see p. 428). 

Stoppers. Those fitted with 514,519, and 524 cones are useful sizes. Stoppers with flat heads are to be preferred, since they may be stood on end when not in pse, thus avoiding contamination of the ground surface. An additional refinement is the provision of a finger grip as in Fig. II, 56,1. 

Mix 50 ml. of formalin, containing about 37 per cent, of formaldehyde, with 40 ml. of concentrated ammonia solution (sp. gr. 0- 88) in a 200 ml. round-bottomed flask. Insert a two-holed cork or rubber stopper carrying a capillary tube drawn out at the lower end (as for vacuum distillation) and reaching almost to the bottom of the flask, and also a short outlet tube connected through a filter flask to a water pump. Evaporate the contents of the flask as far as possible on a water bath under reduced pressure. Add a further 40 ml. of concentrated ammonia solution and repeat the evaporation. Attach a reflux condenser to the flask, add sufficient absolute ethyl alcohol (about 100 ml.) in small portions to dissolve most of the residue, heat under reflux for a few minutes and filter the hot alcoholic extract, preferably through a hot water fuimel (all flames in the vicinity must be extinguished). When cold, filter the hexamine, wash it with a little absolute alcohol, and dry in the air. The yield is 10 g. Treat the filtrate with an equal volume of dry ether and cool in ice. A fiulher 2 g. of hexamine is obtained. 

Dissolve 180 g. of commercial ammonium carbonate in 150 ml. of warm water (40-50°) in a 700 ml. flask. Cool to room temperature and add 200 ml. of concentrated ammonia solution (sp. gr. 0 88). Introduce slowly, with swirling of the contents of the flask, a solution of 50 g. of chloroacetic acid (Section 111,125) in 50 ml. of water [CAUTION do not allow chloroacetic acid to come into contact with the skin as unpleasant burns will result]. Close the flask with a solid rubber stopper and fix a thin copper wire to hold the stopper in place do not moisten the portion of the stopper in contact with the glass as this lubrication will cause the stopper to slide out of the flask. Allow the flask to stand for 24-48 hours at room temperature. Transfer the mixture to a distilling flask and distil in a closed apparatus until the volume is reduced to 100-110 ml. A convenient arrangement is to insert a drawn-out capillary tube into the flask, attach a Liebig s condenser, the lower end of which fits into a filter flask (compare Fig.//, 1) and connect the... 

---