HYDROBROMIC AND HYDRIODIC ACIDS. 
369 
To prepare hydriodic acid, I use the same salt, and follow 
the same mode of preparation, only it is requisite to assist 
the reaction by a little heat. The decomposition is similarly 
expressed by the equation 
Sulphite of soda may likewise be employed for the pre- 
paration of these two gases. With this salt it is not neces- 
sary to add water, as in general the crystals of commerce 
contain a sufficient quantity; I merely dip them in water, 
and then add immediately the bromine or iodine. It is 
necessary to assist the reaction by heat. The reaction is 
very simple. The bromine or iodine decomposes the water 
in presence of this salt; 1 equiv. of hydrogen is transferred 
to the bromine, forming the gas in question, and the oxygen 
converts the sulphite into sulphate: — 
SO 2 , NaO + HO + Br or I=S0 5 NaO+BrH or IH. 
It needs scarcely to be observed that the last method is 
preferable, as the sulphite of soda is commonly met with in 
commerce, whilst the preparation of the hypophosphite of 
lime is very troublesome. In the course of two weeks I 
have disengaged from 20 to 25 litres of these two gases 
without having met with the least accident ; whilst with 
the old process I have frequently had explosions, which 
would certainly have produced serious consequences if the 
quantities operated upon had been at all considerable. 
The proportions to be employed for the preparation of 
these two acids are — 
By the hypophosphite of lime. By the sulphite of soda. 
Water 1 Water 1 
Iodine or bromine . 5 Iodine or bromine . . 3 
Hypophosphite in } Crystallized sulphite } _ 
4l + PhO,CaO+4HO=Ph0 5 +4HI. 
For 10 parts. For 10 pts. 
Chem. Gaz. from Comptes Benclus. 
