ADDENDA. 307 



In 10-15 minutes. Then add 3 grins, of sulphuric acid to the liquid and 

 proceed to add more permanganate in the same manner as before. 



According to Dr. Smith, the oxygen of the permanganate used 'before 

 adding the acid, was taken up by products of putrefaction in solution in 

 the water, such as sulphuretted hydrogen, and that required after the 

 addition of the acid, was consumed by easily oxidizable organic (animal) 

 matter; all matters that thus act speedily on the permanganate are the 

 most harmful in a sanitary point of view. 



. According to this writer and to W. A. Miller also, the results obtained 

 can be expressed more accurately, by giving instead of the number of 

 cubic centimetres of permanganic solution used, the amount of availa- 

 l)le oxygen therein — of which each cubic centimetre contains 0.005 

 grm. 



Dr. Smith estimates the nitrous acid in the water roughly, by di- 

 luting a measured quantity of it until iodized starch i)aper (paper 

 dipped in a solution of potassic iodide containing a little starch) is 

 no longer colored blue by it, even after a contact of several minutes; 

 this diluted solution then contains about one part of nitrous acid in 

 100,000 of water, and upon this basis the proportion in the water 

 before dilution can be estimated. {Chem. News Am. Repr. 5.141, Eny. 

 Ed. 30.113). 



