346 MR. T. CARNELLEY ON A COLORIMETRIC 



XXXIX. On a Colorimetric Method of Determining Iron 

 in Waters. By Thomas Carnelley, B.Sc. Commu- 

 nicated by Professor H. E. Roscoe, F.R.S. 



Eead October 20th, 1874. 



Of late years the analysis of water has become of such 

 importance that any improvement in the methods em- 

 ployed in that analysis will, it is thought, be acceptable, 

 however small such an improvement may be; and it is 

 with this consideration that the following paper is sub- 

 mitted to the Society. 



In the determination of heavy metals in water, with the 

 exception of lead, great inconvenience arises from the want 

 of rapid and accurate methods of estimating very small 

 quantities ; and it is to remedy this inconvenience in the 

 case of iron that the following method is proposed. Be- 

 sides accuracy it fulfils both the other requisites, viz. 

 rapidity and the power of determining exceedingly small 

 quantities; for without any evaporation 1 part of iron in 

 13,000,000 parts of water can be detected, and a deter- 

 mination made in less than fifteen minutes, the smallest 

 amount of ammonia which can be detected by the well- 

 known Nessler test, without concentration, being only 

 1 part of ammonia in 20,000,000 parts of water; and 

 moreover, as water will admit of evaporation without loss 

 of any iron it may contain, the iron which can be estimated 

 may be reduced to almost an infinitely small quantity. 



The method consists in the comparison of the blue 

 colours produced by adding to a solution of potassium 

 ferrocyanide, first, a solution of iron of known strength, 

 and, secondly, the water in which the iron is to be deter- 

 mined. 



