20S Mr, Faradaj/ on the Mutual Action of Sulphuric Acid [Sept. 



Baryta, It is easy by rubbing carbonate of baryta with solu- 

 tion of the impure acid, to obtain a perfectly neutral solution, in 

 which the salt of baryta, containing the acid already described, 

 is very nearly pure. There is in all cases an undissolved por- 

 tion, which, being washed repeatedly in small quantities of hot 

 water, yields to the first portions a salt, the same as that in the 

 solution. As the washings proceed, it is found, that the salt 

 obtained does not burn with so much flame on platinum foil, as 

 that at first separated ; and the fifth or sixth washing will per- 

 haps separate only a little of a salt, which, when heated in the 

 air, in small quantities, burns without flame in the manner of 

 tinder. Hence it is evident that there are two compounds of 

 baryta, which as they are both soluble in water, both neutral, 

 and both combustible, leaving sulphate of baryta, differ probably 

 only in the quantity of combustible matter present, or its mode 

 of combination in the acid. 



It is this circumstance, of the formation of a second salt in 

 small but variable quantities with the first, which must be 

 guarded against, as before-mentioned, in the preparation of salts 

 from the impure acid. It varies in quantity according to the 

 proportions of materials, and the heat employed ; and I have 

 thought, that when the naphthaline has been in large quantity, 

 and the temperature low, the smallest quantity is produced. 

 When the impure acid is used for the preparation of the salts 

 now under description, a small portion of it should be examined 

 by carbonate of baryta, as above, and rejected, if it furnish an 

 important quantity of the flameless salt. 



These bodies may be distinguished from each other provi- 

 sionally, as the Jlaming and the glowing salts of baryta, from 

 their appearances when heated in the air. The latter is more 

 distinctly crystalline than the former, and much less soluble, 

 which enabled me, by careful and repeated crystallizations, to 

 obtain both in their pure states. 



The Jiaming salt, (that corresponding to the acid now under 

 description,) when obtained by the slow evaporation of the satu- 

 rated solution, formed tufts, which were imperfectly crystalline. 

 When drops were allowed to evaporate on a glass plate, the 

 crystalline character was also perceived ; but when the salt was 

 deposited rapidly from its hot saturated solution, it appeared in 

 the form of a soft granular mass. When dry, it was white and 

 soft, not changing in the atmosphere. It was readily soluble 

 in water and alcohol, but was not affiected by ether. Its taste 

 was decidedly bitter. When heated in the air on platinum foil 

 it burnt with a bright smoky flame, like naphthalme, sending 

 flocculi of carbon into the atmosphere, and leaving a mixture of 

 charcoal, sulphuret of barium, and sulphate of baryta. 



After being heated to 212*^ for some time, the salt appeared 

 to be perfectly dry, and in that state was but very slightly hygro- 



