HYDROCHLORIC ACID. 
103 
§ 74-1 
tract, without any relation to poisoning by the free acid ; but in such 
instances it must be rarely, indeed, that surrounding circumstances or 
pathological evidence will not give a clue to the real state of affairs. 
II.—Hydrochloric Acid. 
§ 74. General Properties. —Pure hydrochloric acid is a gas, com¬ 
posed of 97-26 per cent, of chlorine and 2-74 per cent, of hydrogen. 
Commercial hydrochloric acid, muriatic acid, or spiri, of salt is a solution 
of this gas, with more or less impurity, in water. 
Hydrochloric acid is made on an enormous scale in the United 
Kingdom, the production being estimated at about a million tons 
annually. 
The toxicology of hydrochloric acid is modern, for we have no 
evidence that anything was known of it prior to the middle of the 
seventeenth century, when Glauber prepared it in solution, and, in 
1772, Priestley, by treating common salt with sulphuric acid, isolated 
the pure gas. 
The liquid hydrochloric acid of the B.P. has a specific gravity of 
1-16, and contains 31-79 per cent, by weight of HC1. The strength of 
pure samples of hydrochloric acid can be told by the specific gravity, 
and a very close approximation, in default of tables, may be obtained 
by simply multiplying the decimal figures of the specific gravity by 200. 
For example, an acid of 1-20 gravity would by this rule contain 40 per 
cent, of real acid, for -20X 200 = 40. 
The commercial acid is nearly always a little yellow, from the 
presence of iron derived from metallic retorts, and may contain small 
quantities of chloride of arsenic, 1 derived from the sulphuric acid ; but 
the colourless hydrochloric acid specially made for laboratory and medi¬ 
cinal use should be at least of the B.P. standard, the limits being : 
lead limit, 10 parts per million; arsenic limit, 5 parts per million. 
The uses of the liquid acid are mainly in the production of chlorine, 
as a solvent for metals, and for medicinal and chemical purposes. Its 
properties are briefly as follows :— 
It is a colourless or faintly yellow acid liquid, the absence or other¬ 
wise of colour depending on its purity, and especially its freedom from 
iron. The liquid is volatile, and can be separated from fixed matters 
and the less volatile acids by distillation ; it has a strong attraction for 
1 Some samples of hydrochloric acid have been found to contain as much as 4 per 
cent, of chloride of arsenic, but this is very unusual. Glenard found as a moan 2-5 
grammes As 2 0 3 per kilogramme ; but since the mass poisoning by arsenical beer 
derived from glucose made by impure sulphuric acid, English manufacturers have 
succeeded in putting on the market ordinary sulphuric and hydrochloric acids almost 
arsenic-free. 
