OINTMENT OF NITRATE OF MERCURY. 489

Ijondon Dublin Edinburgh United States .

Mercury ... Si- • . • S.i.1 part.Si-

Nitric Acid . . f 3 xj. . . . 3 xiss. [nitrous acid] 2 parts .... t' 3 xi.

Lard .... Jvj. . . . Jiv, ... 3 parts.Jiij.

Olive oil . . . r^iv. . . . Oj. ... 9 parts . Neat’s-foot oil f^ix.

The London Pharmacopoeia directs the solution to be mixed whilehot with the lard and oil melted together. The Edinburgh and UnitedStates Pharmacopoeias order the solution to be added to the mixture oflard and oil when it begins to stiffen.

The theory of the process is as follows :—By the mutual action ofmercury and strong nitric acid, a nitrate of the binoxide, as well as ofthe protoxide of mercury, is formed, while binoxide of nitrogen isgenerated. Part of the latter escapes, and, combining with atmosphericoxygen, forms nitrous acid; the remainder reacts on the free nitric acid,and forms with it hyponitrous or nitrous acid. The liquor then is amixture of nitric acid in excess, probably of nitrous acid , of the nitrateand hyponitrite of the binoxide of mercury , and nitrate of the protoxideof mercury.

When this solution is added to the fatty matter (lard and olive oil), thenitrous acid, or the hyponitrous acid which it contains, converts the oliveoil into a more consistent and less fusible fatty body, which Boudet(Journ. de Chim. Med. viii. 641) calls ela'idine, (from tXaie, cXatciog, anolive tree.) The stearine and elain of the lard also acquire greater con-sistency in consequence of undergoing an analogous change. There is alsoa yellow colouring matter produced, and which may be separated byalcohol. By the saponification of a portion of the ela’idine a smallquantity of mercurial soap (elaidate of mercury) is produced Thelivponitrous acid of the hyponitrite is capable of producing the sameeffect as the free acid.

Boudet is of opinion that these changes are effected by the physicalinfluence of the nitrous acid, for he asserts that the decomposition of theacid is not essential to the formation of the ela’idine. In this I suspecthe is in error.

By keeping, this ointment is apt to become hard, pulverizable, andthereby unfit for use. This depends principally on the change which theolive oil suffers. Hence in the United States Pharmacopoeia neatsfootoil has been substituted for olive oil. The editors of the United States Dispensatory observe, that they had in their “ possession, upwards of fourmonths, a pot of ointment made according to the process of the Pharma-copoeia , and though it had, at the end of this time, partially assumed agreenish colour, it preserved a uniform, soft, unctuous, consistence.”

The fatty bodies exercise a deoxidizing influence on the acids (free orcombined) of the solution, and which is supposed to be independent ofthe formation of ela'idine ; and, in consequence of this, nitrogen orbinoxide of nitrogen is evolved. They also deoxidize the oxides of mer-cury, reducing the binoxide to the state of protoxide, and, in time,converting the protoxide into metallic mercury ; which, being in a finely-divided state, gives to the mass a greyish colour. This latter change isproved by two facts—first, the change of colour which the ointmentundergoes; and secondly, by digesting old citrine ointment in ether, thefatty matters are dissolved, leaving behind metallic mercury.

It is to prevent this change that Guibourt ( Pharm. Raisonnee, ii. 146)