PHARMACY. 
when glazed they are acted upon by che- 
mical agents. The chcinical vessels manu- 
factured by Messrs. Wedgewood are the 
best of this description, except porcelain, 
which is too expensive. 
Glass possesses the three first qualities in 
an eminent degree, and may be heated red- 
hot without mplting. Its greatest incon- 
venience is its disposition to crack or break 
in pieces when suddenly heated or cooled. 
As this is occasioned by its unequal expansion 
or contraction, it is best remeilied by form- 
ing the vessels very thin, and giving them, 
in general, a rounded .shape. Glass vesseh 
should also be well annealed, that is, cooled 
very slowly, after being blown, by placing 
them immediately in an oven while they are 
yet irf a soft state. When ill annealed, or 
cooled suddenly, glass is apt to fly in pieces 
OH the slightest change of temperature, or 
touch of a sharp point. We nray sometimes 
take advantage of this imperfection ; for 
by means of a red-hot wire glass vessels 
maybe cut into any shape. Where there 
is not a crack already in the glass, the point 
of the wire is applied near the edge, by 
which a crack is formed ; and this is 
afterwards easily led in any direction we 
wish. 
- Reaumur’s poi celain is also glass, which, 
by being surrounded with hot sand, is 
made to coOl so slowly that it assumes a 
crystalline texture that destroys its trans- 
parency, but imparts to it every other 
quality desirable in chemical vessels. The 
coarser kinds of glass are commonly used in 
making it ; but as there is no mauufactme 
of this valuable substance, its employment 
is still very limited. 
Lutes also form a necessary part of che- 
mical apparatus. They are compositions of 
various substances, intended to close the 
joining of vessels, to coat glass vessels, and to 
line furnaces. Lutes of the first description 
are commonly employed to confine elastic 
vapours. They should, therefore, possess 
the following properties : viscidity, plasti- 
city, compactness, the power of resisting 
acrid vapours, and certain degrees of heat. 
Tiie viscidity of lutes depends on the pre- 
sence either of unctuous or resinous sub- 
stances, mucilaginous substances, or clay. 
Lutes of the first kind possess viscidity, 
and resist acrid vapours in an eminent de- 
gree ; but they are in general so fusible, 
that they cannot be employed when they 
are exposed even to very low degrees of 
heat, and they will not adhere to any sub- 
stance that is at all moist. The following 
arc a few of this kind that have been most 
frequently employed : 
Eight parts of yellow wax melted with 
one of oil of turpentine, with or without 
the addition of resinous substances, accord- 
ing to the degree of pliability and consis- 
tence required. Lavoisier’s lute. 
Four parts of wax melted with two of 
varnish and one of olive oil. Saussure’s 
lute. 
Three parts of powdered clay worked up 
into a paste, with one of drying oil, or, 
wliat is better, amber varnish. The drying 
oil is prepared by boiling parts of li- 
tharge in 16 of linseed oil, until it be dis- 
solved. Fat lute. 
Chalk and oil, or glaziers’ putty, is well 
fitted for luting tubes permanently into 
glass vessels, for it becomes so bard that it 
cannot be easily removed. 
Equal parts of litharge, qnick-Iime, and 
powdered clay, worked into a paste with 
oil varnish, is sometimes used to daub over 
the cracks in glass vessels, so as to render 
them again fit for some purposes. 
Melted pitch and brick dust. 
Mucilaginous substances, such as flour, 
stai'clr, gnm, and glue mixed with water,witli 
or without some powder-, are sufficiently 
adhesive, ar e dried by moderate degrees of 
heat, and are easily removed after the ope- 
ration, by moistening them with water. 
Brit a high temperature destroys them, and 
they do not resist corrosive vapours. Of 
these take the following forms : 
Slips of bladder macerated in water, and 
applied with the inside next the vessels. 
They are apt, however, from their great 
contraction oir drying, to break weak ves- 
sels. 
One par t of gum arabic with six or eight 
of chalk, formed into a paste with water. 
Flour worked into a paste with powdered 
clay or chalk. 
Alnrond or linseed meal formed into a 
paste wdtlr mucilage or water. 
Quicklime in fine powder, hastily mixed 
with white of egg, and instantly applied, 
sets ver y quickly, but becomes so hard that 
it can scarcely be removed. 
Slaked lime in fine powder, with glue, 
does not set so quickly as the former. 
The cracks of glass vessels are sometimes 
mended by daubing them and a suitable 
piece of linen over with white of egg, strew- 
ing bojh over with finely powdered qrtick 
lime, and instantly applying the linen closely 
and evenly. 
Earthy lutes resist very high tempera- 
