Chap. II.

Acids.

819

the retort ; and if a common retort and receiver be employedfor this distillation, they must not be luted perfectly closely ;for if any portion of the gas should not be absorbed by the wa-ter employed, it must be allowed to escape; but the process willbe performed with greater economy, and perfect safety, in aWoulfe's, or some similar apparatus. The muriatic acid gas,on its condensation, gives out, according to Dr Powell, aconsiderable heat, so that it is necessary to keep the receivercooled during the process.

The residuum in the retort consists principally of sulphateof soda, which may be purified by solution and crystallization ;and to save the retort, Dr Powell directs it to be filled withboiling water, after the process is over, and it has cooled downto 212?:

If properly prepared, the muriatic acid is perfectly colour-less, ami possesses the other properties already enumerated ;but in the shops it is very seldom found pure. It almost al-ways contains iron, and very frequently sulphuric acid or cop-per. The copper is detected by the blue colour produced bysuper-saturating the acid with ammonia, the iron by the blackor blue precipitate formed with tincture of galls or prussiateof potass. The sulphuric acid may be easily got rid of by re-distilling the acid from a small quantity of dried muriate ofsoda. But Mr Hume discovered, that muriate of baryta isprecipitated when poured into pure muriatic acid, from theacid attracting the water of the salt.

Medical use. —In its effects on the animal economy, andthe mode of its employment, it coincides with the acids alrea-dy mentioned, which almost proves, that they do not act byoxygenizing the system. On the contrary, according to SirH. Davy's view of its constitution, it contains no oxygen, andcan only act chemically by imparting chlorine or hydrogen tothe system, or withdrawing from it oxygen or some otherprinciple which has an affinity for chlorine or hydrogen.

AciDUM MURIATICUM DILUTUM. Dub.

Diluted Muriatic Acid.

Take of

Muriatic acid,

Distilled water, each one pound. Mix.The specific gravity is 1080.

This diluted acid of a fixed strength, is convenient for ap-portioning its dose ; and as it is now introduced by the Dub-lin college, it is to be hoped that the same proportions will beadhered to by the others.