308 
ME. W. LASSELL ON POLISHING THE 
a trial- an d-error process as follows: — Take a small sample of the melted pitch, and pour 
it on a thin copper plate. Immerse it in a vessel of water of the probable temperature 
of the apartment in which the polishing-process is to be conducted. When the pitch 
has acquired this temperature, place it on a table, and subject it to the weight of a 
new sovereign placed on edge for sixty seconds. If it receives three clear impressions 
of the milling-strokes in that space of time, it will be about right. It should not 
receive less than 2|- nor more than 3|- strokes. A simple frame should be made to 
hold the sovereign vertically, without influencing its weight. When of right consis- 
tence, the burner should be so regulated that the pitch should not flow too rapidly 
when the plug is partially or wholly withdrawn : indeed, the cooler the pitch, without 
endangering its regular flow, the better ; it will be less liable to adhere to any of the 
moulds when poured into them. The moulds should have been placed, as before 
directed, in cold water, the surface of the water being an inch or two above the tops of 
the moulds. One of the moulds is to be withdrawn from the water, quickly emptied 
by inversion, placed under the side tube of the pitch-vessel, and filled level full of pitch 
by partially withdrawing the plug. The filled mould is then to be sunk just under 
the surface of the water of another vessel and allowed to remain a few minutes. This 
time may be occupied by filling about half a dozen other moulds, when the first will be 
ready to be taken out of the water. On lifting off the zinc hoop and letting down the 
hinged sides, the symmetrical casting of pitch will have become hard enough to drop 
off instantly into the water, leaving the mould quite clean, which should, however, be 
returned to the water before being used again. But little experience will, I think, be 
required to secure this process being carried on easily and successfully. Should a 
single particle of pitch stick to any of the moulds it must he perfectly removed before 
being used again ; and if any of the moulds should give any trouble in this respect, a 
slight touch of rouge on the Avood will probably defend it from the pitch ; but if the 
moulds have been long enough in the water this ought not to be required. The squares 
of pitch must not remain long in contact, even under water, as they are apt to adhere. 
They are best placed, soon after being formed, on a level deal board, the squares just 
covered Avith water, Avhen they Avill take no harm for a considerable time. 
I use the following mode of attaching the squares of pitch symmetrically and firmly to 
the base of the polisher. Fig. 11, Plate 52, represents a piece of stout sheet iron 3^ inches 
broad and about 13 inches long, bent into the form a a, to which is riveted another 
piece (b). The lower part of the upper portion of a is curved into a channel, and a 
sheet-iron cup ( c ) receives any waste pitch Avhich may overflow. The upper part of a 
is heated by a Bunsen burner being placed below it. Three prisms of deal, four tenths 
of an inch square, two of them 12 inches long, the other 24 inches, are to be prepared 
and well soaked in water : these are to be lightly tacked to the base, as shown in fig. 12 
(Plate 50). ' A fourth prism, some 8 or 9 inches long, is also required, and these serve to 
aid in placing the squares correctly and to mark out the interstices between them. 
The fourth prism is unattached, and kept in the hand to mark the separation as each 
