440 Dr, Thomson on [Dec. 



prism was four-sided. The position of the face a was much more 

 oblique with respect to the prism than the face P. Hence it 

 was probably produced by a decrement on the terminating edge 

 of the face M. I coula perceive no corresponding face to a 

 situated on the opposite face of the prism M' ; but this was pro- 

 bably owing to the imperfect state of the crystal. 



The taste of this salt is very acid. When a crystal is held to 

 the flame of a candle, it melts like a piece of ice. It liquifies 

 also when heated on the sand-bath, and remains liquid as long 

 as we please, if the heat does not exceed 300°. When thus 

 treated it loses scarcely any weight. 18*5 grains of the salt 

 dried upon blotting paper were exposed to the flame of a spirit- 

 lamp in a very small platinum crucible, and kept in a red heat as 

 long as perceptible fumes continued to be given out. The salt 

 first melted, then boiled, and gave out copious fumes of sulphuric 

 acid. After some time it became a dry crust, which fused when 

 the heat was increased, and remained in a liquid state during the 

 continuance of the experiment. The loss of weight was 8*1 grs. 

 and the salt still reddened vegetable blues as powerfully as ever. 

 The object of this experiment was to ascertain whether the bisul- 

 phate of soda resembled the bisulphate of potash in the obstinacy 

 with which it retains a certain portion of its excess of acid ; for 

 it is well known that bisulphate of potash cannot be freed from 

 all its excess of acid by heating it over a spirit-lamp. We see 

 that bisulphate of soda is characterized by the same property. 



Specific gravity 1*800. 



A quantity of water saturated with this salt at the temperature 

 of 60 was evaporated on the sand-bath in a glass capsule till it 

 ceased to lose weight. 226*7 grains of water thus treated left 

 109'07 grains of bisulphate of soda. Hence it follows that at 

 the temperature of 60*^, 100 parts of water dissolve 92*72 parts 

 of this salt. It appears from this experiment that bisulphate of 

 soda is more than twice as soluble in water of the temperature of 

 of 60°, as sulphate of soda ; for we learn from Gay-Lussac's 

 table, that 100 parts of water at 60° dissolve only between 38 

 and 39 parts of the crystals of glauber salt. 



To determine the composition of this salt, 20 grains of it were 

 heated in a small platinum crucible over a spirit-lamp (some 

 carbonate of ammonia having been previously mixed with it) till 

 all the excess of acid and water were dissipated, and neutral 

 sulphate of soda remained behind. The weight of this anhy- 

 drous and neutral sulphate was 9*7 grains composed of 



Sulphuric acid 5*377 



Soda 4-322 



9*7 

 Twenty grains of the salt were dissolved in water andprecipi- 



