M Mr." Brown on the Products of the Soda Manufacture. 



12th April, 1848. — The President in the Chair. 



Professor William Thomson read a paper on an absolute thermometric 

 scale, founded on Carnot's theory of the motive power of heat, and 

 calculated from the results of Regnault's experiments on the pressure 

 and latent heat of steam. 



The following paper was communicated by Dr. It. D. Thomson : — 



XL. — On the Composition of the Products of the Soda Manufacture. 

 By Mr. John Brown. 



In the year 1736, Du Hamel proved the base of common salt to be 

 soda. Previous to this, however, Cohausen had mentioned that salt 

 might possibly be decomposed by means of lime ; but as this observation 

 was associated with numerous errors, it was entirely overlooked. In 

 1737 Du Hamel succeeded in obtaining the alkali from sulphate of 

 soda, by fusing with charcoal, and digesting the fused mass in acetic acid, 

 evaporating the acetate of soda thus formed to dryness, and calcining the 

 residue. 



Margraff endeavoured to decompose sulphate of soda by limestone, 

 but without success. In 1768, Hagen showed that salt might be 

 decomposed by means of potash; chloride of potassium and caustic soda 

 being formed. 



Bergmann succeeded in decomposing salt by caustic barytes. 



In 1775, it was shown by Scheele that salt was partially decomposed 

 by oxide of lead. 



In 1782, Guyton and Carny decomposed salt by fusion with felspar. 



Glauber was the first to show that salt could be decomposed by sul- 

 phuric acid, in 1658. 



In 1781, Constantini succeeded in decomposing salt by means of alum* 



The sulphates of lime, magnesia, ammonia, potash, &c. decompose salt, 

 as also iron pyrites. 



To convert the sulphate of soda into caustic or carbonated alkali, was, 

 however, the process of greatest importance. The first step, viz., the 

 conversion of sulphate of soda into sulphuret of sodium, was known to 

 Glauber, Stahl, Du Hamel, Margraff, and others. The difiiculty was to 

 get rid of the sulphur. Du Hamel effected this by means of acetic acid. 

 But in the year 1784, the present process was discovered by Le Blanc 

 and Dize ; and in the beginning of 1791 it was patented by Le Blanc.f 

 He used carbonate of lime to convert the sulphuret of sodium into car- 

 bonate of soda. 



The proportions used by him were — 



* Journal des Mines, Tom. I., No. III., p. 37—69. 

 t Journal des Mines, Tom I., No. VI., p. 6&. 



