"PART III.

Acids. — Acidum Nitricum.

excess of sulphuric acid, which may be dissolved out of theretort by hot water.

By the London process the nitric acid is at first obtainedtolerably free from nitrous oxide; but in genez-al the re-distil-lation, as directed, will be found necessary. In the expulsionof the nitrous oxide, to change the nitrous acid into nitric acid,according to the directions of the Edinburgh College, a portionof the acid is carried over with the gas, as nitrous acid vapour;which should not be wasted, but be condensed by a small por-tion of water being put into the receiver, and thus form adiluted acid. Mr. Murray ' justly observes, that the heat ofa water-bath is best adapted for this operation, being sufficientfor the purpose, and not too great to produce the decompo-sition of the acid. A completely colourless acid, however, isnot obtained, unless the acid be re-distilled from a small portionof black oxide of manganese; but this is not at all necessary formedical purposes. 2

As nitre sometimes contains a small portion of muriate ofsoda, nitric acid, in whatever method it has been procured,may be contaminated with a minute portion of muriatic acid,or of sulphuric acid, if a large proportion of this have been usedfor decomposing the nitre: the presence of the first is detectedby dropping in nitrate of silver, which forms an insoluble mu-riate of silver; while the formation of a precipitate on theaddition of muriate of barytes discovers the second. Thesecontaminations do not affect the medicinal virtues of the acid.

Qualities. — Nitrous acid, as the term is understood in theEdinburgh Pharmacopoeia, is a yellow or orange colouredfluid, emitting, when exposed to the air, deep-orange-colouredextremely suffocating fumes. In its chemical affinities andother qualities it agrees in many respects with nitric acid. Itconsists of nitrous gas loosely combined with nitric acid andwater; and the colour varies according to the proportion ofnitrous gas which is present. From experiments made by SirH. Davy 3 on this subject, the following appear to be the pro-portions in the three states in which nitrous acid is usually pro-cured for pharmaceutical purposes.

100 Parts of Acid.

fpec. Gravity.

Real Nitric Acid.

Water.

. !Nitrous Gas.

Pale yellowBrigiu yellowDark orange

1.502

1 1-500

1-480

90-588-94

86-84

8-3

8-10

7-6

2-002-965-56

1 System of Afateria Medica, ii. 184.

2 Nitric acid was first obtained by Raymond Luily, in the 13th century, by dis-tilling a mixture of nitre and clay : a process still employed on the continent. The«ne Nitric acid was imposed in 1787, by the French chemists,

' ieuarches, 37.

V V