VARIETIES. 
On the Concentration of Sulphuric Acid in Cast-iron Pots. 
By Mr. Roder, Apothecary. — The platina stills used in large 
oil of vitriol manufactories are very costly, and the glass re- 
torts, which were formerly employed for concentrating the 
so-called pan-sulphuric acid, are easily broken and inconve- 
nient. Mr. Roder, apothecary, tried therefore cast-iron 
enamelled pots, and satisfied himself that the enamel was 
not at all destroyed by boiling sulphuric acid. It is well 
known that enamelled vessels suffer much, if the contents 
are evaporated to dryness ; with liquids, however, even if 
they be strong acids, this is not the case, supposing that the 
enamel is very good, and properly fused. 
The enamel of the cast-iron pots employed by Roder was 
prepared in the following manner: — 1 part burnt alum, 4 
parts red lead, 2 parts siliceous earth are ground as finely 
as possible, mixed together, and then fused till the mass 
flows gently; it is then plunged in water and again pul- 
verized. 
Of this powder, fifteen parts are triturated as finely as 
possible with twenty parts of siliceous earth, and three parts 
of tin-ash or oxide of tin, then rubbed down with oil of tur- 
pentine, and applied by means of a soft brush to the interior 
surface of a carefully polished and smoothly turned cast-iron 
pot; the operation is repeated three or four times, but not 
before the preceding coating has become perfectly dry. Pots 
with flat circular bottoms are the best for this purpose. The 
mode of fusing the enamel is known. 
With regard to the concentration of the pan-sulphuric acid 
in these pots on a large scale, the best plan will be to have a 
heating-apparatus for four pots, each for two or three hun- 
dred-weight of acid. Larger pots would considerably in- 
