There are many forms of these, and to describe them would of itself fill a volume. A simple generator for hydrogen sulphide, carbon dioxide or hydrogen is shown in Fig. 106. The acid is held in the bottle, which is provided with a tubulature. The iron sulphide, etc., is in the calcium chloride jar, B. The acid flow is regulated by a Mohr’s clamp, and trickling through the sulphide generates the gas. The spent acid falls into the lower part of the jar and is sucked off into a waste bottle by the siphon, D. The gas is washed by bubbling through water in E and its flow is controlled by the Mohr’s clamp, e.