ANNALS 



OP 



PHILOSOPHY. 



DECEMBER, 1826. 



Article I. 



On Anhydrous Sulphate of Soda, By Thomas Thomson, MD. 

 FRS. Professor of Chemistry, Glasgow. 



There is a manufactory of carbonate of soda near Glasgow, 

 belonging to Mr. Wilson, jun. of Hurlet. The process consists 

 in mutually decomposing protosulphate of iron and common 

 salt. The sulphate of soda thus produced is decomposed and 

 converted into carbonate of soda in the usual manner. Some- 

 time ago they were in the habit of boiling their saturated leys ; 

 during which part of the process large crystals were observed 

 to form in the inside of the boilers. Mr. William Wilson, bro- 

 ther of the proprietor of the work, got a number of these crystals, 

 and from the circumstances of their formation, he concluded 

 that they must be anhydrous sulphate of soda. He was so 

 obliging as to bring me a few of them that their real nature 

 might be ascertained in my laboratory. 



The crystals were octahedrons with a 

 rhombic base of a very large size ; many of 

 them measuring about 1*8 inch in length, 

 and 0*8 inch in breadth. They were 

 translucent, but not quite transparent, and 

 the faces were too rough on the surface to 

 admit of measuring the angles by the 

 reflective goniometer. By a number of 

 measurements with the common goniome- 

 ter, the inclination of 



P on P' is 75° 

 P on V'' 140 



The first of these is the average of 16 measurements never 

 deviating from each other more than 1° ; but the second is the 

 result of one measurement only; for 1 found only a single 

 crystal in which a part of the lower pyramid was visible. In 



^ez(;-Smes, VOL. XII, 2 i> 



