OF WATER FOR ORGANIC MATTER. 71 



^^ We must not, however, forget that if the river is ren- 

 dered impure, the town is proportionately purified. And 

 we must also remember that the work done in the water is 

 enormous. If the refuse matter were allowed to evaporate 

 into the air and so collect its oxygen, the act of purification 

 would go on in the air we breathed ; but now the water 

 draws in oxygen, and as soon as it is consumed it draws 

 in more. Even the air of the river is, at the distance of a 

 few miles down, purer than the air of many towns ; and 

 when the spaces widen, the case is stronger still. 



" I have sometimes inquired if we obtained in fish 

 an equivalent of the manure sent out, and if it is not 

 easier to gather the crop in boats than to put the manure 

 laboriously on land. I find, however, that the loss by 

 putrefaction, oxidation, and evaporation is so rapid that 

 there was no hope of it being used profitably. In one 

 current examined, a very deep one, and much stronger 

 in sewer matter than the Clyde ever is, the whole nitro- 

 gen had disapeared in three days, — the greater part in 

 much less. 



^^ Whilst the chief object of my paper is to show a new 

 mode of examining climate as well as streams, I am glad 

 to be able to say that Glasgow has failed to destroy the 

 purity of the Firth beyond the points indicated, and that 

 we may still rejoice in our summer dwellings. It is, how- 

 ever, not to be forgotten that the eff'ects are found too far 

 away, and that twenty-two miles of mischief is more than 

 abundance. It is to be hoped that the cautious policy of 

 the city in waiting for the best method to be adopted for 

 using its refuse will enable it to carry out that future 

 work, whatever it may be, with the greatest success. 



" I have referred only to the 1st column. It indicates 

 the amount of permanganate decomposed instantly; this 

 represents the gases of decomposition, such as most readily 

 pass into the atmosphere. 



" It will not be supposed that this is the only ofiensive 

 matter. 



"The 2nd column represents the amount when acid is 



