636

ELEMENTS OP MATERIA MEDICA.

2. The employment of a proper quantity of acid. —In the process of the Lon-don College, by which, when it is strictly followed, a veryfine product is obtained,acid of a sp. gr. of 1-5 is directed to be used. But tbe sp. gr. of commercial nitricacid rarely exceeds 1-38 or 1-4. Hence, therefore, a larger quantity of commercialacid is required to be equivalent to the quantity of strong acid ordered by the Phar-macoposia.

3. Stirring assisis the evolulion of gas, and is usually belicved to favour theformation cf a fine product. —Mr. Alsop, however, asserts that a long continued

stirring is not required.

Properties. —When fresh prepared, this ointment has a fine golden yellow colour,a butyraceous consistence, and a remarkable nitrous odour. It is very apt to be-come gray when mixed with other ointments, in consequence of their deoxidizingpowers. It should be spread with wooden or ivory spatulas.

Composition. —When fresh prepared this Compound contains the following sub-stances:—

Elaidine.

Red Oil.

Elaidate of mercury (mei'curiui soap.j

Nitrate of Mercury.

Eldidine is a white saponifiable tat, fusible at 97°F. [896 F. according to Meyer,]

r soluble in ether, but requiringIt consists of elaidic acid and

(Pkarmaccutisches Central-Blatt für 1840, S. 790.) very soluble in ether, but requiring200 times its weight of boiling elcohol to dissolve it. Tf »-»■»«*■ «» «uu;« on ;^ aj

glycerin.

Physiological Effects.- —It is an irritant and slight caustic. When it hasnndergone decomposition by keeping, it irritatcs ulcers exceedingly, and evenexcites slight erysipelatous inflammation.

Uses. —We employ it as a stimulant and aiterative in chronic diseases of theshin, more particularly those affecting the hairy scalp, as the different forms ofporrigo, in which it is exceedingly efficacious. It is also used as a dressingto ulcers —to stimulate and cleanse them—as in foul syphilitic sores and phage-denic ulcers. Lastly, it is employed in Ophthalmie diseases —more particularly Oph-thalmia tarsi, or psorophthalmia, in which it is applied (mixed with its own weightof almond oil) by means of a camel's-hair pencil to the lids, frequently with suchadvantage that some have regarded it as a specific in this complaint.

18. HYDRAR'GYRI ACE'TAS, D.— ACETATE OF MERCURY.

History. —This Compound was known to Lefebure in the 17th century.Preparation. —In the Dublin Pharmacopaia the directions for procuring it arethe following:—

Take of Parified Mercury, Acetate of Potash, of eaeh nine parts; Diluted Nitric Acid,eleven parts; Boiling Distilled VVater, one hundred parts; Distilled Vinegar, as much as maybe sufficient.

Let the Nitric Acid be added to the Mercury, and when tbe effervescence has ccased, let themixture be digested that the metal may be dissolved : let the Acetate of Potash be dissolvedin water, arid let the distilled vinegar be added until the acid shali predomiuate in the liquor;to this, whilst boiling, let the Solution of the Mercury in the Nitric Acid be added, and let tbemixture be filtered as quickly as possäble through a double linen cloth; let it cool that crys-tais may form ; having washed these with cold distilled water, dry them on paper with a verygentle beat. In every step of this process let glass vessels be employed.

By the mutual action of diluted nitric acid and mercury we obtain a protonitrateof mercury (vide p. 607.) When this is mixed with acetate of potash double decom-position takes place: nitrate of potash and protoacetate of mercury being formed.To prevent preeipitation of the yellow subnitrate of mercury, excess of acetic acidshouid be employed: and by filtering, whilst hot, any which may be formed wouldbe separated before the acetate has deposited.

Properties. —This salt oecurs in white micaeeons, flexible scales, which areinodorous, but have an acrid taste, li bläckens by Hght When heated it is re-r