CHEMICAL MANUFACTURES ON THE TYNE. 133 



powder, bicarbonate oi soda, oxycbloride of lead and other products. 

 The methods generally adopted in condensing are well known, and 

 we shall only allude to some of the improvements practically applied. 

 The drying furnace usually used is what is called an " open furnace," 

 to which the heat of the fire is directly applied, and we believe that the 

 greatest difficulties in the way of a perfect condensation in former times 

 arose with the gases from this furnace. The heat required to drive 

 off the gas from the crude sulphate of soda is very great, and when 

 the gases arrived in the condensers it was found difficult to absorb 

 them, even when a very large quantity of water was used, and the 

 muriatic acid which was thus produced was of so low a strength that 

 it was commercially almost useless. In former years, also, the draught 

 through the condensers was always obtained by a connection with a 

 high chimney, but in some of the works this plan is now abandoned, 

 and the whole of the vapour or gas which escapes passes through a 

 12-inch pipe always open to view. At present these gases are con- 

 ducted through long flues or pipes and cooling shafts, and on entering 

 the foot of the condensers the heat is reduced to about 140 deg. Fah., 

 at which point the gases easily condense, and a strong acid is at the 

 same time obtained. A rather different method has been pursued for 

 some time at Messrs. Allhusen and Son's works. Instead of the heat 

 from the fire being conducted directly on to the drying materials in the 

 furnace, which is generally done, a " close furnace " is used, in which 

 the flame from the fire passes over a brick arch and under the bed of 

 the furnace, and not in immediate contact with the materials. This 

 furnace has no connection with a chimney for its draught, and the 

 gases from both the pan and dryer pass into one condenser. The 

 hydrochloric acid passes off from the furnace unmixed with the smoke 

 from the fire, and at a lower temperature than by the ordinary method, 

 and is consequently more easily condensed, and obviates the necessity 

 of long flues or cooling shafts. Messrs. C. Allhusen and Sons have 

 given us the following results of some recent experiments with this 

 class of furnace. The charge of salt usually used was 8 cwt., the moisture 

 varied from 6 to 9 per cent., and the sulphate of soda contained from 

 175 to 2-25 per cent, of undecomposed salt : — 





Salt unde- 

 composed. 



Moisture 

 per 

 cent. 



Theoretic 

 weight 

 of Acid. 



Acid ob- 

 tained. 



Loss 



per 



cent. 



1st Experiment 



1-75 



7-0 



502-0 



495-06 



1-4 



2nd 



1-70 



7'0 



498-0 



489-00 



1-8 



3rd 



2-25 



7-0 



498-0 



484-08 



2-6 



4th 



1-80 



7-0 



498-0 



49004 



1-6 



5th 



1-70 



7-0 



498-0 



485-00 



2-6 



Average . . . 2-0 



