230 Anhydrous Crystals of Sulphate of Soda. [1828. 



part of the chlorine had acted upon the alkali to form chloride 

 and chlorate. 



21. It would seem as if I were unacquainted with Dr. Gran- 

 ville's paper upon this subject, in the Quarterly Journal of 

 Science, p. 371, were I to close my remarks without taking 

 any notice of it. Unfortunately Dr. Granville has mistaken 

 M. Labarraque's direction, and by passing chlorine, to " com- 

 plete saturation," through the carbonate, instead of using the 

 quantities directed, has failed in obtaining Labarraque's really 

 curious and very important liquid ; to which, in consequence, 

 not one of his observations or experiments applies, although 

 the latter are quite correct in themselves. 



Royal Institution, Sept. 3, 1827. 



Anhydrous Crystals of Sulphate of Soda*. 



IF a drop of a solution of sulphate of soda be placed upon 

 a glass plate and allowed to evaporate spontaneously, it will 

 leave crystals which may be distinguished by their form and 

 ultimate efflorescence, as being the salt in question. Most of 

 the potash and soda salts may be distinguished as to their base 

 by such an experiment. They are easily converted into sul- 

 phates by a drop or two of sulphuric acid and ignition, and 

 then, being dissolved and tried as above, will yield crystals 

 which may be known by their forms, and more especially 

 by their efflorescence if of soda, and their unchangeable state 

 if of potash. This test is, however, liable in certain circum- 

 stances to uncertainty, arising from a curious cause. If the 

 drop of solution on the glass be allowed to evaporate at common 

 temperatures, then the efflorescence takes place and the dis- 

 tinction is so far perfect ; but if the glass plate with the drop 

 upon it be placed upon a warm part of a sand-bath or hot iron 

 plate, or in any other situation of a certain temperature, con- 

 siderably beneath the boiling-point of the solution, the crystals 

 which are left upon evaporation of the fluid are smaller in 

 quantity, more similar in appearance to sulphate of potash, and 

 finally do not effloresce. Upon examining the cause of this 



* Quarterly Journal of Science, xxv. 223, 



