and the Cunstituents of fFell- and River-waters. 55 



the one great objection to this water for domestic purposes, 

 namely its organic impurities. 



lu my previous paper, ah'eady referred to, I pointed out, that, 

 from the united influence of heat and contact with the copper of 

 the still, nitrite of ammonia was produced duriug the distillation of 

 Thames water. From analogy, it was assumed that iron would 

 possess the same power of converting the nitrogen of the organic 

 matter, or the ammonia resulting therefrom, into nitrous acid. 

 With the view of deciding this important question, I made com- 

 parative experiments on the Thames water, as supplied by the 

 Grand Junction Company to my laboratory, before and after 

 being exposed to the action of a large surface of iron. The 

 method adopted of testing for nitrous acid was as follows : — The 

 residue of each gallon of water was introduced into a Florence- 

 flask furnished with a cork and funnel-tube. In the neck of the 

 flask was placed a slip of bibulous paper moistened with starch- 

 paste and iodide of potassium. Ten cubic centimetres of water 

 were added to each flask to cover tbe bottom of each of the funnel- 

 tubes. To each flask were now added 10 cubic centiois. of dilute 

 sulphuric acid (made by mixing 10 cubic centims.of pure HO,SO^ 

 with 90 cubic centims. of water). No indications of nitrous 

 acid were in either experiment obtained, since the paper in each 

 flask remained perfectly white*. Six other gallons of water, 

 drawn at the same time, were placed in open glass bottles, and 

 to each gallon was added two ounces of coiled iron wire. Each 

 bottle was left during forty-eight hours. Phjenomcna were 

 observed similar to those noticed in the case of the Amsterdam 

 water, but the deposit was of a browner colour. After filtration 

 the water was found to be perfectly bright, and as colourless as 

 distilled water. Each gallon was separately evaporated to dryness, 

 aud the residues tested, as above described, for nitrous acid: — 



Exp. L Paper became blue in ten minutes, and intensely blue 



in one hour. 

 Exp. TI. Paper blued in five minutes. 

 Exp. III. Paper blued in four minutes. 



As it appeared probable that the nitrous acid liberated by the 

 sulphuric acid miglit remain in solution, and in consequence 

 not instantly affect the test-paper, in experiments with the resi- 

 dues of the other three gallons of the water which had been in 

 contact with iron, 1 used hot water and an acid of double 

 Ktrength. In each experiment tlie test-paper became blue in a 

 few seconds. 



Tiiese experiments prove, I believe, beyond a doubt, the pro- 



* These experiiiicnts were iiiaile in very eolil wciitlier. 



