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35
To sum up, I find that a mixture of 5 grains to the gallon
of lime, and 2½ grains to the gallon of ferrous sulphate give
better results than even Dr. Tidy's recommendation of 10 grains
of lime, and 7 of alumina.
The cost of lime is about £1 per ton.
„ protosulphate of iron „ £2 5s. „
„ alum „ £2 10s. „
and the suggestion will effect a considerable saving in the outlay
upon chemical precipitants.