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LECTURES TO SCIENCE TEACHERS. 



unequal expansion, and as soon as a crack occurs, the hydro- 

 chloric acid gas is pulled or drawn by the draft of the 

 chimney through that crack, and then passes up the chimney, 

 where the pressure is somewhat less than that of the atmo- 

 sphere, and is delivered into the air, rather than through the 

 condensers, where the pressure is somewhat greater than the 

 atmosphere. This is a fertile source of annoyance in the 

 neighbourhood of alkali-works, and one which it is difficult 



*" Seduonal Plans tivro. A.J3 



for the inspector to calculate for. Several suggestions have 

 been made with the view of obviating this difficulty in the 

 use of the closed roasters. 



One of the most feasible and ingenious of the proposed 

 schemes is that patented by the late Mr. Deacon, of Widnes. 

 You see in the drawing that the fireplace is built contiguous 

 to, but several feet below the brick chamber or muffle 

 in which the acid gas is evolved. It follows from this 



