82 Mr Cameron on a nexn) method of making Crucibles. 
tion. Having found it to be the opinion of my friends that the 
process should not be lost, I have been induced to draw up the 
following account of it for the Edinburgh Philosophical Journal. 
For each of the different sizes of the crucibles, I formed ten 
or twelve dozen of moulds of stucco, burnt and powdered in 
the usual manner. For the first mould of each ‘ size, I formed 
a piece of soft pipe-clay into the shape of the intended crucible, 
and laid it with its mouth downwards on a flat surface, and in- 
' . ... 
closed it with a cylinder of white-iron, distant about half an 
inch from the angular points of the crucible, and about an inch 
and a lialf higher than its bottom ; then, mixing the stucco 
with water, poured it into the cylinder. When the stucco was 
sufficiently set, I removed the white-iron, picked out the clay, 
and dried the mould ; I then squeezed soft clay into the mould, 
which, on standing a few' minutes^ easily came out again. It 
was inclosed in the c}dinder, and stucco poured round it, which 
formed a second mould, continuing to do so until I had procur- 
ed the number wanted. They w^ere then all put into a stove, 
and completely dried ready for use. 
In the preparation of the fire-clay for the crucibles, I follow^- 
ed precisely the same process used at the potteries, by mixing it 
with a very large quantity of water, and putting the whole 
through a No. 9. silk search. On allowing the whole to stand 
a few hours the clay subsided, and in pouring off the clear wa- 
ter, I procured the clay or slip of the consistence of thick 
cream. On w^eighing a gallon of it, I found the proportion of 
clay it contained, and added sand to the whole, in the propor- 
tion of seven of sand to seventeen of clay : I then stirred and 
mixed the whole completely, when it was ready for use. I next 
took my moulds, previously dried, and arranged them in pa- 
rallel rows on a table, and successively filled them with the pre- 
pared slip. By the time I had filled four or five dozen, I re- 
turned to the one first filled, and began alternately to pour the 
slip out of them, leaving a small quantity unpoured out, which 
subsided, and gave the requisite thickness to the bottom. In 
each of the moulds so filled, a crucible is completely formed by 
the abstraction of the water of the slip, in contact with, and ad- 
joining to, the porous substance of the stucco mould. The cru- 
cible will bn either thicker or thinner in proportion to the time the 
