he advantages afforded by
the locality, but the amount of expense will be very differently
thought of by different persons: one will be content with any moderate
arrangement which will answer the purpose, where another will be
scarcely satisfied unless everything is quite of an _orne_ character.]

_Dr. Diamond's Replies._--I am sorry I have not before replied to the
Queries of your correspondent W. F. E., contained in Vol. viii., p. 41.;
but absence from home, together with a pressure of public duties here, has
prevented me from so doing.

1st. No doubt a _small_ portion of nitrate of potash is formed when the
iodized collodion is immersed in the bath of nitrate of silver, by mutual
decomposition; but it is in so small a quantity as not to deteriorate the
bath.

2nd. I believe collodion will keep good much longer than is generally
supposed; at the beginning of last month I obtained a tolerably good
portrait of Mr. Pollock from some remains in a small bottle brought to me
by Mr. Archer in September 1850; and I especially notice this fact, as it
is connected with the first introduction of the use of collodion in
England. Generally speaking, I do not find that it deteriorates in two or
three months; the addition of a few drops of the iodizing solution will
generally restore it, unless it has become rotten: this, I think, is the
case when the gun cotton has not been perfectly freed from the acid. The
redness which collodion assumes by age, may also be discharged by the
addition of a few drops of liquor ammoniae, but I do not think it in any way
accelerates its activity of action.

3rd. "Washed ether," or, as it is sometimes called, "inhaling ether," has
been deprived of the alcohol which the common ether contains, and it will
not dissolve the gun cotton unless the alcohol is restored to it. I would
here observe that an excess of alcohol (spirits of wine) thickens the
collodion, and gives it a mucilaginous appearance, rendering it much more
difficult to use by its slowness in flowing over the glass plate, as well
as producing a less even surface than when nearly all ether is used. A
collodion, however, with thirty-five per cent. of spirits of wine, is very
quick, allowing from its less tenacious quality a more rapid action of the
nitrate of silver bath.

4th. Cyanide of potassium has been used to re-dissolve the iodide of
silver, but the results are by no means so satisfactory; the cost of pure
iodide of