ily decomposed nature; while if the pictures are
passed through a solution of alum after washing and fixing, the gelatine
also is so acted upon as to be rendered in a great degree impervious to
the action of damp, and the pictures are then somewhat similar to carbon
pictures without carbon.

I may now say a few words on the defects and failures sometimes met with
in working this process; and first in regard to the yellowing of the
whites. I hear frequent complaints of this want of purity in the whites,
especially in vignetted enlargements, and I believe that this almost
always arises from one or other of the two following causes:

First. An excess of the ferrous salt in the ferrous oxalate developer;
and when this is the case, the yellow compound salt is more in
suspension than solution, and in the course of development it is
deposited upon, and at the same time formed in, the gelatinous film.

The proportions of saturated solution of oxalate to saturated solution
of iron, to form the oxalate of iron developer, that has been
recommended by the highest and almost only scientific authority on the
subject--Dr. Eder--are from 4 to 6 parts of potassic oxalate to 1 part
of ferrous sulphate.

Now while these proportions may be the best for the development of a
negative, they are not, according to my experience, the best for
gelatine bromide positive enlargements; I find, indeed, that potassic
oxalate should not have more than one-eighth of the ferrous sulphate
solution added to it, otherwise it will not hold in proper solution for
any length of time the compound salt formed when the two are mixed.

The other cause is the fixing bath. This, for opals and vignetted
enlargements especially, should always be fresh and pretty strong, so
that the picture will clear rapidly before any deposit has time to take
place, as it will be observed that very shortly after even one iron
developed print has been fixed in it a deposit of some kind begins to
take place, so that although it may be used a number of times for fixing
prints that are meant to be colored afterward it is best to take a small
quantity of fresh hypo for every enlargement meant to be finished in
black and white. The proportions I use are 8 ounces to the pint of
water. Almost the only other complaints I now hear are traceable to
over-exposure or lack of intelligent cleanliness in the handling of the
paper. The operator, after having been dabbling for some time in hypo,