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bodies [^known to the chemist, would immediately vanish 
into the river again, NOW in the form of phosphoric acid. 
After this it might recombine with calcium or magnesium, 
and await a second metamorphosis. Regarding the sul- 
phuretted hydrogen at the period of Lyon Playfair’s investi- 
gation, I cannot of course dispute it directly, but I state 
most emphatically, that if the river bed were of the same 
composition as it is at the present day, and if the vegetable 
dyes, &c., turned into the river then, were at all like those 
turned into the river to-day, that it would he almost 
impossible for sulphuretted hydrogen to be given off in the 
form of gas from the water, because it is now a well-known 
fact that the oxide of iron largely present in the mud of the 
Irwell and its tributaries, coupled with the large amount of 
iron present in solution in the water (derived from dye- 
works, chemical works, paper works, &c,,) combines with it 
when in the status nascendi,” forming ferrous sulphide. 
This black compound enters largely into the constitution of 
the mud of sewage polluted streams, and I know from a 
long series of examinations of the mud of the Irwell at 
Throstle Nest, that ferrous sulphide is largely present in the 
mud. I have analysed repeatedly, at various times in the 
year, gas collected from the Irwell at spots immediately above 
the Weir at Throstle Nest, below it at the place where all the 
water samples were taken during 1883, 1884, 1885, and at 
Barton above the locks. At the first mentioned locality an im- 
mense evolution of gas is to be often seen during the summer 
months, but I can say without hesitation that it contains no 
traces of sulphuretted hydrogen, having tested it many times 
for that gas, and never detected the slightest trace. The 
gas thus rising to the surface varies very much in compo- 
sition at different places. That coming to the surface at the 
Throstle Nest Weir containing a large quantity of carbon 
dioxide and a small quantity of “marsh gas” (CH4), whereas 
