CARBOLIC ACID PLASTER. 
391 
be not used in the manufacture. When the litharge and olive-oil are in the 
proportions directed by the Pharmacopoeia, a certain quantity of water must be 
added to promote the combination of the fatty acids with the oxide of lead, and 
even then the process is a very tedious one. But it is an interesting fact, 
chemically, that if the litharge is used in about four times the Pharmacopoeia! 
proportion, although no water be employed, the combination proceeds under a 
brisk heat with great rapidity. It is upon this fact the following method of 
manufacture is based :— 
“ Take of 
Olive-oil 12 parts (by measure). 
Litharge (finely ground), 12 parts (by weight). 
Beeswax, 3 parts (by weight). 
Crystallized carbolic acid, : l\ parts (by weight). 
Heat half the olive-oil over a slow fire, then add the litharge gradually, stirring 
constantly till the mass becomes thick or a little stiff ; then add the other half 
of the oil, stirring as before, till it becomes again thick. Then add the wax 
gradually, till the liquid again thickens. Bemovc from the fire, and add the 
acid, stirring briskly till thoroughly mixed. Cover up close and set aside, to 
allow all the residual litharge to settle; then pour off the fluid, and spread 
upon calico to the proper thickness. The plaster made in this way can be 
spread by machine, and kept rolled in stock ; and, if in a well-fitting tin canister, 
will retain its virtues for any length of time.” 
But for almost all purposes the antiseptic lead plaster is superseded by his 
lac plaster, which is made in this manner :— 
“ Take of 
Shellac, 3 parts. 
Crystallized carbolic acid, 1 part. 
Heat the lac with about one-third of the carbolic acid over a slow fire till the 
lac is completely melted ; then remove from the fire and add the remainder of 
the acid, and stir briskly till the ingredients are thoroughly mixed. Strain 
through muslin, and pour into the machine for spreading plaster ; and, when 
the liquid has thickened by cooling to a degree ascertained by experience, spread 
to the thickness of about one-fiftieth of an inch. Afterwards, brush over the 
surface of the plaster lightly with a solution of gutta perch a in about 30 parts 
of bisulphide of carbon. When the sulphide has all evaporated, the plaster 
may be piled in suitable lengths in a tin box, without adhering, or rolled up and 
kept in a canister.” The coating of gutta percha, through which the acid per¬ 
meates freely, is given to prevent it adhering to the skin, as “it is desirable 
that such a dressing should adhere very slightly, if at all. It has this great 
advantage over the antiseptic lead plaster, that it cannot be softened either by 
a watery or an oily fluid.” If made to contain much less than 25 per cent, of 
the acid, it is brittle, but this may be avoided by the addition of spirit of wine 
in an equivalent quantity, as this sample contains 12 a per cent, of acid and the 
same of spirit. 
These plasters are generally kept applied to the part by means of ordinary 
adhesive plaster strapped round the edges of the piece employed. But to avoid 
any chance of germs getting access to the wound, to the adhesive plaster befoio 
spreading, he directs 1 per cent, of carbolic acid to be added. 
Many other applications are used in this system of treatment, but these plasters 
being interesting pharmaceutical preparations, I have thought worthy of bring¬ 
ing under your notice this evening. 
The samples exhibited were prepared in the Hospital Dispensary. 
University College Hospital, Dec. 2, I8G8. 
