H. Wurtz on the Preparation of Pure Sulphates. 367 
This production of caustic soda may be advantageously carried 
on in connection with the manufacture of a better quality of 
soda ash by a method sometimes resorted to. A solution of car- 
bonate of soda cannot be made stronger than 32° B. Accord- 
ingly the crude soda lye when evaporated retains in solution all 
the caustic soda and sulphid of sodium and deposits a very good 
carbonate which is dipped out, drained, and calcined for soda 
ash. When the liquor shows by increasing in density beyond 
32° B. that the carbonate has all fallen, it can be transferred to 
other kettles, evaporated till it gets very dense, and then mixed 
with oxyd of iron and dried yea he roasted product will 
give a good caustic. soda by solution, decantation, evaporation, 
fusion and deflagration. « 
Art, XLI—On the Preparation of some Pure Sulphates, and 
particularly of Sulphate of Copper; by Henry Wurtz, Prof. 
Chem. National Med. Coll., Washington. 
(Read before the American Association for the Advancement of Science, at 
Baltimore, April, 1858.) 
ComMERCTAL blue vitriol always contains sulphate of protoxyd 
rated b stallization, owing to 
the fact, determined by Mitscherlich,* that ferrous sulphate, 
_ «* cd & of 
carbonate of baryta. ‘The hot solution is then fil 
to ¢ ize, when large ¢ of 
are obtained, containing no trace of iron.t Deutoxyd of lead is 
prepared for this purpose by boiling minium with dilute nitric 
i inium itself, if free from 
or acetic acid in the usual way, but minium itse 
* Gemlin’s Handbuch, iii, 461. + Specimens were exhibited to the Section 
