70 
THE GEOLOGIST. 
heat, till the lead is all oxidised. The advantages of the bone 
ash over the mica sometimes employed are manifold. 1. It is 
easier to be obtained, and everywhere the operator can prepare 
a little if he should not be supplied with it. 2. The metal will 
remain in the concavity of the bone ash paste, and not be liable 
to run down and be lost, as on the mica. 3. It is never neces- 
sary to change the material ; the bone ash absorbs the litharge 
which collects on the mica, and impedes the process, so that the 
remaining metallic globule has to be transferred to a fresh slip 
of mica. 4. The colour of the paste, after the operation is 
finished, gives an indication as to the nature of some impurities 
of the metal ; lead alone makes it appear yellow ; a small pro- 
portion of copper changes the yellow colour to greenish. — Dr. 
G. Engellmann. 
Manufacture of Sulphuric Acid from Gypsum. — Thaulow has 
proposed the following method for preparing sulphuric acid in 
large quantities from gypsum. The gjrpsum is reduced in iron 
or earthern retorts by heating with charcoal ; the carbonic acid 
v/hich is evolved is not suffered to be lost, but is preserved for 
further use. The sulphuret of lime is mixed with some water 
and the carbonic aoid gas passed into it ; the sulphuretted hy- 
drogen which evolves is conducted into leaden chambers, and 
there first bui'nt to water and sulphurous acid, and this latter 
oxidised in the usual way. — Archiv. de Fharm, 
Ox- Acids of Sulphur, — Specimens of a new ox-acid of sulphur 
were submitted to the Paris Academy of Sciences; this acid, 
having for its formula S*^ 0^, has been named by the discoverers 
MM. Fordos and Gelis, bisulphuretted hyposulphuric acid. It 
completes, according to them, a curious series of the ox-acids of 
sulphur, the quantity of oxygen remaining constant, whilst that 
of sulphm- increases according to the numbers 3, 3, 4, thus : — 
Sulphuric acid, 0^ S^ ; sulphuretted hyposulphuric acid. 0^ ; 
bisulphuretted hyposulphuric acid, 0^ S"*. MM. Fordos and 
Gelis have succeeded in isolating their new acid, as also some of 
