230 Miscellaneous Intelligence. 
the traces of the glass rod, in consequence of the expulsion of 
carbonic acid by the heat disengaged by friction.” 
6. On the Uses of Sulphate of Lead in the Arts.—Those dyers 
and calico-printers who prepare their aluminous mordaunt 
by decomposing alum by acetate of lead, obtain at the same 
time a large quantity of sulphate of lead. M. Berthier, in a 
paper published in the Annales de Chimie et Physique, has de- 
tailed the various uses which may be made of this product. 
In the first place, it may be reduced into metallic lead. When 
sulphate of lead is heated to redness with a sufficient quantity 
of charcoal powder, half the sulphuric acid which it contains is 
converted into sulphurous acid, and the sulphur belonging to the 
other half forms a subsulphuret with the lead. The sulphurous 
acid carries with ita portion of the subsulphuret in the state of 
vapour, When the heat is carried beyond redness, the sub- 
sulphuret is decomposed, and changed into another sulphuret, 
which is volatilized, and into lead which remains mixed with 
the undecomposed subsulphuret. The higher the temperature, 
the greater the loss of lead by volatilization. 
100 grains of sulphate of lead, mixed with 9 grains of char- 
coal, and heated in a retort, gave out sulphurous acid gas for 
half an hour; a scoriform mass of subsulphuret of lead re- 
mained, and carbonic acid and oxide were also evolved. 
10 grains of sulphate of lead, heated for half an hour in a 
coated crucible, in a calcining furnace, yielded a metallic sco- 
ria weighing 7.1 gr. It consisted of 0.4 sulphur and 6.7 lead. 
Sulphate of lead only contains 0.683 of metal, so that very little 
was volatilized. 
These, and similar experiments, shew that, by uniting sul- 
phate of lead with about one-tenth its weight of charcoal, it is 
converted into subsulphuret without material loss of weight. 
This subsulphuret may be treated as galena, and the lead 
easily extracted. But there is a simple and more economical 
means of reducing sulphate of lead. Sulphate and sulphuret 
of lead may be made mutually to decompose each other, and if 
mixed in proper proportions pure lead is the result. Pure lead 
may also be obtained from a mixture of sulphate and subsul- 
phuret of lead, as the following experiment proves. 20 grains 
of sulphate, mixed with 29 grains of subsulphuret, were heated 
to whiteness in an earthen retort; pure sulphurous acid was 
evolved, and a button of ductile metallic lead, weighing 38 grs., 
was obtained, covered with a thin crust of vitrified oxide. As 
the original mixture only contained 40 grains of lead, it 
will be observed that the entire loss of metal in the above re- 
duction amounted to five per cent. only. If sulphate of lead 
be heated with such proportion of charcoal as is insufficient to 
reduce it entirely to sulphuret, that portion of sulphuret which 
