THE RIVER IRWELL AND ITS TRIBUTARIES. 251 



facturers are doing nothing. In Table " B " I give the 

 percentage of volatile organic matter present in lOO parts 

 of the respective amounts of 'Hotal matter in solution.^^ 

 By treating the analytical data in this manner a very fair 

 opinion can be obtained as to the pollution of a stream 

 like the Irwell. I have made similar calculations in re- 

 gard to streams which were only polluted with what is 

 known as " domestic sewage/^ and always found that the 

 total matter in solution in the water contained from 27 to 

 60 per cent, of volatile organic matter ; and^ further, that 

 this excessive amount of organic matter rapidly preci- 

 pitates out on being exposed to the air. This precipitation 

 of the organic " sewage matter " in solution is well illus- 

 trated in the analysis of the Irwell at Throstle Nest and 

 the Irwell at Barton (in Table "D"). It will be seen, 

 on calculating out the percentages, that the Irwell at 

 Throstle Nest contains 37*5 per cent, of volatile organic 

 matter in 100 parts of its '"total matter in solution,^' 

 whilst at Barton the same water contains only 17-61 per 

 cent, of volatile organic matter in lOo parts of its "total 

 matter in solution.^^ Exactly one-half of the organic 

 contamination has been precipitated out of the water in the 

 flow from Throstle Nest to Barton. 



Regarding the method of analysis of the waters, I may 

 say that I consider Frankland^s process quite useless by 

 itself in ascertaining the state of the pollution of a river 

 in a manufacturing district, because it cannot discriminate 

 between the pollution by sewage and the pollution by 

 manufacturer's waste waters. By adopting a parallel test- 

 ing of the water by the processes of Wanklyn and Tidy, 

 a very good idea is obtained of the state of the water, 

 especially if these two processes are supplemented by 

 the determination of the amounts of chlorine, volatile 

 matter in both " suspended matter '' and " matter in solu- 

 tion.^^ I always filtered the water, and considered the 



