ON MURIATIC ACID. 
223 
being, therefore, considered pure enough, it was employed 
in some qualitative analyses. On directing, however, the 
practical chemical manipulations, I had frequent occasion 
to remark that, from completely pure metallic salts, the 
acidulated solutions of salts which are not precipitated by 
sulphuretted hydrogen, yet on being acidulated with the 
above muriatic acid, a black precipitate was invariably 
thrown down. This observation naturally raised the sus- 
picion, that the hydrochloric acid contained a body causing 
the said precipitate ; I, therefore, examined the acid more 
minutely. Several experiments showed, that the hydro- 
chloric acid contained chloride of lead, in no inconsiderable 
quantities. The precipitate thrown down by sulphuretted 
hydrogen which was brown-red at first, and on employing 
an excess of the latter body turned black, was sulphuret of 
lead. On diluting the acid with water, small shining leaf- 
lets of chloride of lead, were gradually deposited, owing to 
the greater solubility of this salt in the concentrated acid 
than in water. The crystals easily fuse before the blow- 
pipe, and on being calcined with soda, the metallic lead is 
reduced ; and by being moistened with hydrosulphate of 
ammonia they become black. With sulphuric acid a white 
precipitate is thrown down in the acid. Potassa and am- 
monia throw down a precipitate, which on account of the 
traces of iron admixed is somewhat yellowish. 
To determine the amount of chloride of lead contained 
in the acid, one ounce of the same was slowly evaporated 
to dryness. The dry residue weighed 4.75 grammes, which 
corresponds nearly to 1 per cent. 
The presence of chloride of lead in hydrochloric acid, 
may easily be accounted for, since, in some manufactures? 
as is known, the decomposition of common salt, and the 
distillation of the acid is effected in leaden vessels. 
Very distinct crystals of chloride of lead may be obtained 
by evaporating the acid to one-third of its volume, when, on 
cooling, this salt is deposited in large quantities. Hydra- 
