226 DR. DAUBENY ON THE OCCURRENCE OF IODINE AND BROMINE 
accompanying Table, which shows that the proportion of iodine to chlorine 
varies in every possible degree, and that the springs most strongly impregnated 
with common salt are in some instances those in which I have evaporated the 
largest quantity without detecting any trace of iodine. The same remark will 
equally apply to bromine ; so that the general inference seems to be, that 
although these two principles may perhaps be never entirely absent where the 
muriates occur, yet that their distribution is certainly very unequal, and there- 
fore forms a proper subject of scientific research. The quantity in which the 
former of these ingredients occurs in mineral waters is commonly so incon- 
siderable, that I have been unable to determine it by direct analysis, and have 
been therefore obliged to content myself with obtaining an approximation to 
its real amount. In the case of one of the Leamington springs, indeed, I em- 
ployed the agency of nitrate of silver to precipitate the iodine from the con- 
centrated water, and afterwards separated by means of ammonia the chloride 
from the iodide of silver obtained. I have reason, however, to believe, from 
some comparative experiments, that where the proportion which this latter 
ingredient bears to the former one is extremely small, it may be taken up 
either wholly or in part by ammonia ; and I therefore contented myself in 
other instances with evaporating the water until it began to produce the cha- 
racteristic blue or violet tinge with starch and sulphuric acid. This was then 
compared with the colour imparted by the same test to a solution of hydrio- 
date of potass of known strength ; and the latter, if not of the same shade 
already, was brought to it by dilution with a measured quantity of water. 
Having thus noted the proportion of iodine in the test liquor with which .the 
concentrated solution corresponded, it was easy to calculate what it must have 
been in the mineral water itself, by knowing the number of times its original 
quantity had been reduced by evaporation previously to the employment of 
i 
this re-agent. 
The sulphates and muriates present in brine-springs do not appear to inter- 
fere with the delicacy of this test ; but where bromine was also present, I have 
portion of iodine in sea-water, although I have reduced ten gallons of it, taken from the English 
Channel near Cowes, to less than half an ounce, without being able to detect any in the residuum. 
There seems reason, however, to infer, from what is stated in the next page, that the starch test can- 
not br relied upon to detect very minute quantities of iodine, when a comparatively large proportion 
of bromine is present in the same solution. 
