By Catalytic Union of the Elements

The catalytic method6,7 for the preparation of hydrogen iodide with the subsequent absorption of the gas in water to form hydriodic acid has the advantage that a very pure product of any desired concentration up to that of the fuming acid may be prepared in a single operation. 

The amount of iodine placed in the bulb and the volume of water initially in the absorption vessel will 

The vessel C may be replaced by two empty gas-washing bottles so arranged that the gas enters through the short arm, and D may be replaced by the more conventional type of gas-absorption vessel in which the gas enters through a tube with a funnel-shaped orifice dipping slightly below the level of the liquid. If a cylindrical vessel is used, it may conveniently be graduated so the density of the acid can be estimated quickly. 

Iodine may be regarded as the chief impurity likely to be present, but the acid obtained should be only slightly colored by dissolved iodine. When not objectionable, the acyl may be stabilized as described in procedure A. 

Blanchard and Phelan Synthetic Inorganic Chemistry, 3d ed., p. 122, John Wiley Sons, Inc., New York, 1922. 

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