Chemical lecture experiments . th water. The whole apparatus is firmly supportedon the ring of a retort stand. On removing the plug fromthe end of the tube dipping underwater no action takes place, as thereis a long layer of air in the tube be-tween the ammonia and water. Onpinching the bulb of the dropper afew cubic centimeters of water aresuddenly introduced into the flask,and absorption is instantaneous, thevacuum produced being sufficient tocause the water to ascend the longtube and play out of the jet as afountain. The alkalinity of the wateris strikingly shown by the change incolor of th
Chemical lecture experiments . th water. The whole apparatus is firmly supportedon the ring of a retort stand. On removing the plug fromthe end of the tube dipping underwater no action takes place, as thereis a long layer of air in the tube be-tween the ammonia and water. Onpinching the bulb of the dropper afew cubic centimeters of water aresuddenly introduced into the flask,and absorption is instantaneous, thevacuum produced being sufficient tocause the water to ascend the longtube and play out of the jet as afountain. The alkalinity of the wateris strikingly shown by the change incolor of the litmus solution. In case the flask has been com-pletely filled with gaseous ammonia,water will rush in till the flask isfull. Provision must be made for theaddition of water to the crystallizing dish as fast as it is withdrawn. The support must be strongenough to hold up the flask when filled with 2 1. of water. 2 1. flask (dry) ; 2-holed cork and jet; medicine dropper; NH3generator ; soda-lime drying-tube ; litmus Fig. 84 24. Collection over mercury and absorption by water. — Gaseous ammonia, owing to its great solubility in water, canbe collected only over mercury. Dried gaseous ammoniais collected in a thick-walled test-tube over mercury, carebeing taken not to have the deli very-tube dip too deeplyinto the mercury, thereby increasing the pressure to be over-come. The great solubility of ammonia is seen when a fewdrops of water are allowed to enter the tube through a 196 CHEMICAL LECTURE EXPERIMENTS hooked glass tube and to rise through the mercury andcome in contact with the gaseous ammonia. The absorptionis very rapid, the mercury rising in the tube to take theplace of the absorbed gas. A piece of ice may be used instead of water. Mercury trough ; NH3 supply ; ice. 25. Preparation of ammonium hydroxide (ammoniawater). — Ammonium hydroxide is prepared by saturatingwater with gaseous ammonia. Ammonia gas is generated as in Ex. 19, and conducteddirectly from
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