PATENT. Ill 
ART. XXVIII.— PATENT GRANTED TO PAUL GILBERT PRE- 
LIER, FOR IMPROVEMENTS IN THE MANUFACTURE OF 
DRY SULPHURIC ACID AND NORDHAUSEN SULPHURIC 
ACID. 
The patentee commences his specification, by stating 
that, in consequence of the great alEnity of sulphuric acid 
for water, it is difficult to concentrate the acid even to 66° 
B.; therefore, in order to obtain dry sulphuric acid, he com- 
bines simple sulphates with a fresh proportion of acid for 
the purpose of forming bisulphates, which he decomposes 
by the action of heat, and thus obtains dry sulphuric acid. 
The manufacture of sdry acid naturally leads to tlie pro- 
duction of smoking or Nordliausen sulphuric acid, as the 
latter is formed by the addition of dry acid to sulphuric 
acid which has been concentrated to 66°, the specific 
gravity of the Nordhausen acid increasing with the quantity 
of dry acid added. 
In carrying out the invention, the patentee prefers to 
employ 100 parts sulphate of soda, 2 parts sulphate of pot- 
ash, and 2 parts sulphate of lime ; but these proportions 
may be varied ; and even if sulphate of soda alone be em- 
ployed, dry sulphuric acid will be obtained. The mixture 
is put into freestone retorts, set in a suitable furnace; then, 
by means of a bent glass tube, the acid is introduced into 
the retorts, and heat is gradually applied. Shortly after the 
application of heat, drops of water will proceed from the 
retorts, then acidulated water, followed by acid at 40°, 50"^, 
and 66°, and finally by acid which fumes or smokes. To 
enable the operator to judge correctly as to the progress of 
the operation, vessels containing water are placed to receive 
the drops of acid ; and when each drop produces a sound 
resembling that which would result if a red-hot iron was 
