342 LECTUBES TO SCIENCE TEACHERS. 



a fact this process is not usually worked in England, and it 

 becomes a question whether some process of this kind may 

 not, with advantage, be more generally adopted as a pre- 

 ventative against the evolution of sulphuretted hydrogen. 



Another sulphur-recovery process, which is particularly 

 applicable to the treatment of the alkaline drainage from old 

 waste-heaps, is that proposed by Mr. Mactear. The yellow 

 liquors thus obtained are mixed with lime and submitted to 

 the action of sulphurous acid. Sulphur is then deposited, 

 and calcium hyposulphite formed, whilst some sulphuretted 

 hydrogen is given off. To this liquor, fresh yellow-liquor is 

 added in suitable proportions, so that on the addition of 

 hydrochloric acid no sulphuretted hydrogen is evolved, but 

 only sulphur deposited. 



Out of the very many proposals which have been made to 

 replace Leblanc's original reactions by others, only one has 

 been practically successful. This is theoretically a very 

 simple and beautiful one, and in skilful hands has been 

 found capable of being worked on a manufacturing scale. 

 I have here a solution of brine, such as is obtained by pump- 

 ing from the Cheshire salt-beds in Northwich. This I 

 saturate with ammonia gas, and into the brine thus saturated 

 I pass a current of carbon-dioxide. After a short time you 

 observe that a white precipitate falls ; this white precipitate 

 consists of bicarbonate of soda. Nothing can surely be 

 simpler or more beautiful than this no evolution of noxious 

 fumes, no waste of sulphur ; by a simple decomposition we 

 at once obtain what we want ; thus : 



NH 3 + C0 2 + NaCl + H 2 = NaHC0 3 +NH 4 Cl. 



The precipitate consists of bicarbonate of soda insoluble in 

 the ammoniacal brine, whilst sal-ammoniac remains in the 

 liquid, and from it the ammonia can be recovered by heating 

 the liquor with lime. Simple and beautiful as this process 

 appears to be, the difficulties which surround it are extremely 

 great. Although there is doubtless a future for this process 

 it is very unlikely that it will interfere with the manufac- 

 ture of soda by the old plan. One reason against the pro- 

 cess is, that in the old process the manufacturer not only 

 makes use of the sodium of the common salt, but likewise 

 of the chlorine ; indeed in many alkali-works the maimfac- 



