[1. Both papers are equally available for both purposes. In actual
practice we have not ourselves experienced any difference in their
results.
2. It is quite immaterial. A drachm of bichloride dissolved in one
ounce of spirits of wine will cause a cloudiness and a precipitate, if
a very few drops are added to the tested water.
3. In general the salts of iron are more adapted for positives, and
weak pyrogallic acid solutions for negatives; say one and a half grain
of pyrogallic acid, twenty minims of glacial acetic acid, and an ounce
of distilled water.]
* * * * *
Replies to Minor Queries.
_London Fortifications_ (Vol. ix., p. 174.).--In last week's Number is an
inquiry as to "London Fortifications" in the time of the Commonwealth.
There is a Map by Vertue, dated 1738, in a folio _History of London_; there
is one a trifle smaller, copied from the above; also one with page of
description, _Gentleman's Magazine_, June, 1749. I subscribed to a set of
twenty etchings, published last year by Mr. P. Thompson of the New Road;
they are very curious, being facsimiles of a set of drawings done by a
Capt. John Eyre of Oliver Cromwell's own regiment, dated 1643. The drawings
are now I believe in the possession of the City of London.