[Illustration: Fig. 155. A. The iron mortar containing the phosphorus and chlorate of potash. B. The pestle, with the shield, C C, composed of a circle of wire gauze, covered with one of cardboard.] _Eighth Experiment._ Phosphuretted hydrogen owes its property of spontaneous combustion to the presence of the vapour of a liquid, phosphide of hydrogen (PH_{2}), which may be prepared by placing some phosphide of calcium into a flask with water heated to a temperature of 140° Fah., and conveying the gas into a U-shaped tube surrounded with a mixture of ice and salt. The liquid obtained is colourless, and must be preserved from contact with air, as it takes fire spontaneously directly it is exposed to the atmosphere. (Fig. 156.) [Illustration: Fig. 156. A. The flask containing the phosphide of calcium and water, and placed in a water-bath heated to 140° Fah. B. Bent tube conveying the gas to C C, the U-shaped tube, to which it is attached by india-rubber tubing, C C. The U-shaped tube, surrounded with a freezing mixture. D D. Bent tube, passing into a cup of water to prevent contact with air.] [Page 171] _Ninth Experiment._ Phosphide of calcium is quickly prepared by placing some small pieces of lime in a crucible and making them red-hot; if lumps of dry phosphorus are thrown into the crucible, and the cover placed on quickly, and immediately after the phosphorus, the latter unites with the calcium, and forms a brown substance which produces gaseous phosphide of hydrogen (PH_{3}) when placed in water, and the gas takes fire spontaneously when it comes in contact with the air. _Tenth Experiment._ Phosphorus placed in a retort with a tolerably strong solution of potash, and a small quantity of ether, affords a large quantity of phosphide of hydrogen (commonly called phosphuretted hydrogen) when boiled. The neck of the retort must dip into a basin of water, and the object of the ether is to prevent the combustion of the first bubbles of gas _inside_ the retort, which by their explosion would probably break the glass. If the neck of the retort is kept under water in which potash is dissolved, the gas may be generated for many days at pleasure, although it is not a desirable experiment to renew too often, on account of the disagreeable odour produced. (Fig. 157.) [Illustration: Fig. 157. A retort containing the phosphorus, water, potash, and ether. B. Neck dipping into a basin of water. C. The gas burning, and producing beautiful rings of smoke.] _Eleventh Experiment._