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. Granville'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 "complete saturation," through the carbonate, instead of using the quantities directed, has failed in obtaining Laharraque'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[1].
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 sulphates 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 circumstances 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 distinction 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, considerably 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.
