230 DR. DAUBENY ON THE OCCURRENCE OF IODINE AND BROMINE 
of the ingredients given by that able chemist, in consequence of the weaker 
impregnation of the samples of water I employed, than of those on which he 
appears to have operated. 
It will be seen by reference to the Table, that all the brine-springs of that 
district contain bromine, and most of them iodine ; indeed it is probable that if 
I had had time to concentrate larger quantities of the water, the latter would 
have been detected throughout. It may be remarked, however, that the rock- 
salt of Northwich in Cheshire contains no trace of either principle ; a circum- 
stance explicable from the more deliquescent nature of the hydriodic and 
hydrobromic salts, which would cause them, together with the earthy muriates, 
to remain in the mother-liquor after the common salt had crystallized, and thus 
to become distributed through the substance of the marly beds afterwards 
formed over the rock-salt, from which the brine-springs appear to derive their 
saline impregnation. 
There is a blue variety of rock-salt met with at Ischel near Saltzburg, which, 
from the resemblance between its colouring matter and that of the compound 
of starch and iodine, might be suspected to contain this latter principle united 
with some kind of vegetable matter. I have been unable to obtain a specimen 
deeply enough tinged with the colouring matter alluded to, to set the question 
completely at rest ; but on dissolving a portion of the blue salt, which I obtained 
through the kindness of Mr. Heuland, in water, not the slightest tinge appeared 
to be communicated to the solution, neither did any blueness appear on re-cry- 
stallizing the salt. The specimen alluded to gave no indications of iodine when 
tested with starch in the usual manner, and was nearly pure from admixture 
with foreign ingredients, although it appeared to contain a trace of sulphuric 
acid and of lime. At present, therefore, I am inclined to attribute the colour 
rather to some peculiar arrangement of the particles of the common salt itself, 
than to the presence of any other ingredient. 
The springs containing purgative salts, which arise from the lias clay in 
various places along its whole range from Leamington to Gloucester, appear 
to be derived from the same source as the brine-springs of Cheshire and Wor- 
cestershire above alluded to ; but their saline contents have been modified by 
the sulphuric acid generated by the decomposition of the sulphuret of iron 
present in the stratum from which they immediately proceed. Hence the pro- 
