420 BULLETIN OF THE UNITED STATES FISH COMMISSION. 
There are paper-mills on the Hudson from Troy up to Jessup’s Landing, 
both numerous and large, but in ail of them that I visited I was told 
that the use of chloride of lime had decreased to a mere fraction of 
what was formerly employed. In these mills wood-pulp is the basis of 
paper, and it does not require the bleaching that other materials do, 
and, as one manufacturer said, “ We do not use as much chloride of 
lime in a month as we did in a day before we began using wood-pulp, 
and you will find that this is the rule with all the paper-mills.” In con- 
versation with other paper manufacturers they confirmed this state- 
ment, and therefore there is now less than 4 per cent, of poison from the 
paper-mills than there was before wood-pulp was used to make paper. 
DAMS AND OBSTRUCTIONS. 
The first obstruction that a salmon meets in the Hudson is the State 
dam at “Troy, which barred their ascent until in June last, when a rise 
in the river gave 2 feet of water oil the crest of the dam, and some sal- 
mon went over it. These are the fish referred to above, seen at Me- 
chanicsville. The State legislature made an appropriation for a fishway 
in this dam, and one was built last summer after the salmon run was 
over, by the McDonald Fishway Company. After the completion of 
this fishway I was in Troy, but the water was too high to see the struct- 
ure, which, I am informed, is substantially built, and is complete in 
all respects. This form of fishway differs in principle from all others, 
and from a study of fishways in Europe and America I believe it to be 
the best in use. I have drawings of all the different fish passes in the 
world, some of which have never been published, and some of them 
are very odd. When in charge of the department of American fish- 
culture at the International Fisheries Exhibition, held at Berlin in 
1880, 1 gathered a mass of material, which was never published because 
the Government did not issue a report of that exhibition, and among 
my sketches are some odd fishways in the English department. Allow- 
ing me to judge, I will say they were, some of them, of a most primi- 
tive sort, and of little use to most fishes. I merely cite this to show 
that I have paid attention to the construction of fishways, and have a 
knowledge of the principles of all the different fishways, without pro- 
fessing to know anything about the practical building of one. From a 
study of working models I am satisfied that the McDonald fishway is the 
easiest of ascent of any. I have seen a model of a catamaran actually 
go up one by the force of the side currents, while the water in the mid- 
dle of the fishway was a turbulent rapid, gradually working down, but 
checked at every foot into a semblance of a mountain torrent. 
I think, and so said in print a dozen years ago that fish will find the 
entrance to a fishway with greater certainty if it is at the foot of the 
dam, instead of below it, and would therefore advocate the building of 
a fishway above the dam, if possible to do so. 
Mechanicsville .— The dam at this place is 9 miles above the Troy dam, 
