the Ferrocyanide of Potassium in Chemical Analysis. 221 
Though this process appears a long one, from the details which 
are necessary to explain its principle, yet in practice it is very ex- 
peditious, and requires only a very few minutes for its performance, 
and is much quicker than either Gay-Lussac’s or Otto’s method. 
Though I have as yet chiefly confined my attention to the 
use of the ferrocyanide of potassium in the estimation of 
chlorme in bleaching powder, I have no doubt that it may 
be advantageously employed in many other useful determinations 
by carrying out the principles already explained: thus, for 
example, it may be used as a means of determining the amount 
of bichromate of potash present in a sample of that salt, or 
the quantity of chromic acid that exists under different circum- 
stances. Again, the same salt may be used in different deter- 
minations where a certain amount of chlerine is liberated, which 
represents a proportional quantity of some other substance: thus, 
for example, in the estimation of manganese ores for commercial 
purposes, where they are heated with hydrochloric acid, the 
quantity of chlorine disengaged will indicate a certain amount 
of peroxide of manganese in the ore, on the presence of which 
its commercial value almost entirely depends ; and the chlorine 
evolved may be estimated by absorbing the gas in a dilute 
solution of caustic potash, and then determining the amount of 
chlorine in it by precisely the same process as that I have re- 
commended in the valuation of chloride of lime. To test the 
accuracy of this method, I heated in a small flask a given 
quantity of pure bichromate of potash with an excess of strong 
hydrochloric acid, and collected the evolved chlorine by means 
of a dilute solution of caustic potash, employing the bulbed 
retort and curved dropping tube as recommended by Bunsen in 
the “‘Analysis of the Chromates” (see the last editionof Fresenius’s 
‘Quantitative Analysis,’ page 234), and ascertained afterwards, by 
the use of the ferrocyanide of potassium, the amount of chlozine 
evolved, which corresponded almost exactly with the calculated 
amount of that substance which should have been obtained by 
the action of the quantity of bichromate used on the hydrochloric 
acid. Again, a standard solution of ferrocyanide of potassium 
may be used, as i. de Haen has shown, to determine the strength 
of the permanganate of potash in the analyses of the ferrocyanide 
and ferrideyanide of potassium, as an acidified solution of the 
ferrocyanide, as before stated, rapidly decolorizes a solution of 
permanganate of potash, whereas the ferrideyanide has no 
action on that salt; and this reaction might be taken advantage 
of, in the valuation of chloride of lime, to determine the excess 
of ferrocyanide used in my process: but from my experiments 
I found that more precise and accurate results were obtained by 
the use of the bichromate of potash. 
