By CORROSION. 379 
difficulty. It would be well to furnith it with a proper 
cover to reftrain the acid fumes from efcaping. I have 
always ufed a cover of cork lined with wax, into which, 
whilft it is in a melted ftate, the inferior fide of the cover 
may be dipped; and this cover muft be cut fo as to fit ex- 
aatly the mouth of the veffel. The great advantage of a 
glafs veffel over the others is its tranfparency, whereby 
we are able to fee how the corrofion goes on, and to judge 
when it is finifhed. This takes up from fix or feven days 
to a fortnight or three weeks, according to the nature of 
the part to be prepared, and to the quantity and concen- 
tricity of the menftruum employed, in which it ought to 
be entirely covered. When the acid is very dilute, it proves 
rather antifeptic and a preferver of animal fubftances, than 
a corrofive menftruum. 
Of difengaging the Corroded Subftance. 
Fifthly. The laft part of the operation confifts in difen- 
gaging the loofened and corroded fubftance from that of 
the injection. In this piece of bufinefs we ought to take 
the greateft care, if we wifh to avoid breaking down the 
beautiful {mall veffels of the part. With this view the acid 
fpirit employed as a menftruum fhould be decanted from 
the inje@tion with great caution, whenever the corrofion 
of the furrounding fubftance is complete, fo that it no 
longer adheres to the veffels. In place of the corroding 
menftruum, foak the preparation in {imple water for three 
or four days. The loofe fubftance may be removed from 
the veflels, by pouring frefh water over the preparation 
flowly, and in fmall quantity at a time; or otherwife we 
may put the preparation in a veflel pierced with holes, 
like a cullender, and place this in fuch a manner as to 
receive a gentle current or {tream of water. If we fhould 
place the veflel near the nofel of a pump, and under the 
droppings or f{malleft {tream which we can procure to fall 
from it, the preparation may be thus cleanfed from the 
joofe corroded matter with which it is encompafled. 
But 
