438 Dr, Thomson on [Dec. 



Tlie specific gravity of the salt at 63*^ was 2*26. I determine 

 the specific gravity of salts insoluble in alcohol by filling a nar- 

 row graduated tube with alcohol to a certain point. Into this a 

 given weight of the crystals (say 40 grains) is put, and the bulk 

 of this weidit is determined by observing how much the surface 

 of the alcohol is elevated. From this, knowing the weight of 

 100th part of a cubic inch of water at 62° to be 2*5272 grains, it 

 is easy to deduce the specific gravity of the salt. Thus if 40 

 grains of a salt were equivalent to the bulk of 10-lOOths of a 

 cubic inch, or to 25*272 grains of water, its specific gravity 

 would be 1-58. 



At the temperature of 63°, 100 parts of water dissolve about 

 25 parts of this salt. The crystals were previously reduced to 

 powder, and the solution was accomplished by agitating 100 

 parts of water with 10 parts of salt in a glass tube. As soon as 

 the first 10 parts of the salt had dissolved, 10 more were added. 

 Twenty parts treated in this manner dissolved completely ; but 

 when about the half of the third 10 parts was dissolved, crystals 

 began to form in the liquid, and to subside in it. This put a 

 stop to the process. The crystals were doubtless common sul- 

 phate of soda; for we learn from M. Gay-Lussac's experiments, 

 that at the temperature of 64°, 100 parts of water dissolve only 

 16*73 parts of anhydrous sulphate of soda. But 25 parts of ses- 

 quisulphate of soda contain 19*5 parts of anhydrous sulphate. 

 Accordingly when we separate the sulphate of soda from the 

 liquid by crystallization, a very acid liquid remains behind. 



When sesquisulphate of soda is heated on the sand-bath, it 

 does not melt nor alter its appearance, and loses very little 

 weight : 40 grains, when treated in this way, sustained a loss of 

 1*2 grain. Even when heated to redness in a platinum crucible, 

 the loss of weight was inconsiderable. It was, therefore, mixed 

 with a sufficient quantity of carbonate of ammonia, and heated 

 over a spirit-lamp, till it ceased to give out any thing. Forty 

 grains of it when thus treated lost 8*7 grains of weight. The 

 residual 31*3 grains proved on examination to be anhydrous 

 sulphate of soda. Composed of 



Sulphuric acid 17*38 



Soda 13*91 



31*30 



Forty grains of the crystals of sesquisulphate of soda were 

 dissolved in water, and precipitated by muriate of barytes. The 

 sulphate of barytes obtained, after being washed, dried, and 

 exposed to a red heat, weighed 75 grains, equivalent to 25*42 

 grains of sulphuric acid. 



If from 25*42 w^ subtract 17*38, the quantity of acid in 

 40 grains of the salt when converted into neutral anhydrous sul- 



