to powder, put it into a thin glafs phial, for the thin-
nter it is, the lefs liable to break k, then place it in an
iron veffel, filled with fand, fo that the neck of the phial
may be open, and the bottom not in conta<ft, with
that, of the veffel, then put it into a common kitchen
oven : all the arfenic will evaporate at the neck of the
phial, and the cobalt will be purified. After this pro-
cefs, it flill preferves its grey colour, and, mixed with
fand, and the afhes c f foda and barrilla, is what the
Saxons call zaffre ; this mixture is made, becaufe fand
and quartz, are infufible, without the affiftance of barrilla,
or fixed alkali ; but with it, they foon vitrify, and communicate
the fame property to the cobalt. If this zaffre
is melted with a vitreous fritt, it changes into a blue glafs,
called fmalt, when in maffes, and azure, or enamel blue, when
reduced into a fine powder, ufed by painters, for that
beautiful blue on porcelain, and in other manufactures [a].
In the effays made on Spanifh cobalt, in Germany, it
appeared to be entirely free from foreign matter, and fo
(a) Mr. Bowles in a note Ends fimh'w'ith the Ericyeidpedie, and other writers on chemiftry,
for faying, that the cobalt and zaffre o f the Eaft, are nearly exhaufted, and that we have na
foundation for fuch an affertion, and ought rather to apply the inferiority o f thyir modern colouring,
to their craft, on finding us fo eafily fatisfied. But the principal reafon given by
thefe. writers, is, on acfcount o f the confiderable quantity o f zaffre and fmalt now exported from
Europe to. China,, which Mr. Bowles takes no notice oft Zaffre has been thought o f fuel
nfe in'England, that the fociety for the encouragement of arts, manufaftures and commerct
promired in i j 55,’ a premium o f $ oil for making the moft and bell zaffre, and fmalt from Eng-
110, cobalt, not left than 51b. weight of zaffre, and 15U). o f fmalt to be produced before the
fociety, with fatisfattory certificates. • t .
rich, o f the blue colouring earth, that it imbibed three
or four times more fand or quartz, than, that of Saxony.
About the year 1746, it was a great faihion, in Paris, to
make fympathetic ink. I fet about making o f it, as well
as the reft, and gave nine livres (a) for a pound of Spa-
niih cobalt, with which I made my ink, which was more
efteemed, than any they had feen, the green colour being
much more lively, than if made with the cobalt of Saxony.
The Spanifh mineral has not even the grey colour
o f the Saxon, but is blue, like melted lead, infomuch
that in feveral manufadures, and particularly that o f Count
Aranda for delf-ware, at Alcora, in Valencia ; they ufe it
without any other preparation than pulverifing the ftone,
as itis taken out o f the mine, and with this blue powder
in its natural ftate, they paint the ware without further
procefs (b).
(a) A b o u t feven {hillings and fix-pence fferling.
(i) Cobalt has been found in Cornwall and Scotland, and probably in other parts o f Europe,
o f various colours and hues, mixed with different fubftances, which mineralifts have
fully defcribed, particularly Cronfted. Wallerius enumerates fix different (pedes thereof.
I f well calcined cobalt be treàted with inflammable matter, and fluxed like other metallic
calxes, it will be reduced to a femi-metal, called b y Mr. Brandt,of the Swedilh academy^
who firft produced it, regulu, o f M l . This regulus, and alfo the calx o f cobalt, am o n g * .
other Angular properties, makes fympathetic ink, b y being diffolved in aqua regia. This in k
may be applied to the drawing o f laadfcapes, in which the ground and trees are deftimte o f
verdure, being firft drawn with Indian ink, giving an appearance o f winter ; but thofe parts,
coffered' with this preparation,' referable the fpring, on being expofed to a gentle heat, when
the green leaves appear on the trees, and thegrafs in the fields, which idea has been executed
in France by an ingenious artift On a fire-fcreen ; and as a folutiou o f regulus o f cobalt, or o f
zaffre, in fpiri,| o f wine, acquires a reddilh .colour b y application o f heat, more variety may
* 1 1 be introduced in the landfeape, and fruits'¡rad flowers fuddetily brought out, by the red
foiutiob, at the faiae time that the leaves and verdure appeared whh the g te en .-— D iil. o f
chemiilry.
E e 2 L E T T E R