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Scientific Intelligence. 
among the industrious classes of society. A leading object of 
the Society will be to erect a hall for depositing instruments, 
and models of machinery of all kinds. 
40. Method of taking Impressions of Gems and Seals in 
Shell-lac. — Take a piece of mica, and put some lac upon it; 
hold it over the fire till the lac is softened, which must then be 
spread evenly over the mica : on the surface of the lac put a 
piece of gold-leaf or coloured foil, about the size of the impres- 
sion to be taken ; and cover this also with a thin layer of lac : 
it must now be softened at the fire, and the impression taken as 
with sealing-wax. The lac takes a very sharp impression ; and 
the reflection from the gold-leaf gives the figures a fine relief. 
The mica is convenient for melting the lac upon, and the im- 
pression easily separates from it, leaving the back with a fine 
shining surface, and beautiful iridescent colours, occasioned by 
a thin plate of the mica adhering to the lac. The same piece 
of mica may be used for many impressions. In softening the 
Tac, the heat should not be so strong as to make air-bubbles rise, 
as it is difficult to get quit of them again. 
41. Glass from Straw.-— 'Wheat straw may be melted into a 
colourless glass with the blowpipe, without any addition. Bar- 
ley straw melts into a glass of a topaz-yellow colour. 
4^2. Experiments on the Colour of Minerals. — The Yellow 
Carnelian may be changed into a fine red, by exposing it in a 
crucible with sand to a heat under redness. In India, the 
stones are put into an earthen-pot, and covered with six inches 
of dry goafs dung : fire is then applied ; and in twelve hours 
the pots are sufficiently cool to be removed.” Black Rock-crys- 
tal may be made quite colourless by heat. Some specimens 
may be obtained of a yellow colour by not continuing the heat 
too long. The colour of the Amethyst may be taken away by 
a moderate heat : if the heat be increased, it becomes white and 
opalescent. The amethyst is more apt to crack with the heat 
than rock-crystal. The Beryl is changed with a moderate heat 
to a light blue : when the heat is raised, it becomes like mother- 
of-pearl. The Emerald has the same kind of pearly lustre when 
heated. The colour of the Chrysoberyl is not altered with a 
red heat. Dr Clarke exposed a Diamond of an amber colour 
