boiling the water the carbonic acid gas is expelled
and the iron salt is precipitated from solution. The removal of this
and some other objectionable salts which the water very probably
contains, may be removed by the addition of the proper quantity of
clear lime water to it--the lime in this instance will combine with
the excess of carbonic acid and fall to the bottom together with the
carbonate of iron. To determine the precise quantity of lime water
requisite, add the reagent (saturated solution) to a small portion (of
known volume) of the freshly drawn water, in small quantities at a
time, and with constant stirring until no further precipitate forms.
Then by a simple operation in proportion the quantity of the reagent
necessary for the purification of a given quantity of the well water
may be easily determined. An excess of the reagent must be avoided.
This impurity would probably prevent the successful working of an
injector.

W.S.W. asks: How is the best rosin, used on violin bows,
prepared?--W.F. asks: What is a simple method for washing clay for
brick and tile making?--E.S.D. asks: What is the best kind of wood to
construct a guitar?

* * * * *

COMMUNICATIONS RECEIVED.

The Editor of the SCIENTIFIC AMERICAN acknowledges, with much
pleasure, the receipt of original papers and contributions upon the
following subjects:

On Rheumatism. By A.R.E.
On Postage Stamps. By E.B.
On Boiler Explosions. By G.B.B.
On Reaching the North Pole. By J.H.S.
On Heating Street Cars. By P.T.
On a Hybrid Fruit, By R.S.B.
On an Air Vessel. By J.T.R.

Also inquiries and answers from the following:
E.B.M.--F.F.F.--N.B.H.--B.B.--O.F.--R.V.J.--F.M.--N.B.C.--C.F.E.--W.T.
--C.W.C.--T.F.--C.A.S.--S.N.M.--J.R.D.--P.J.D.S.

* * * * *

HINTS TO CORRESPONDENTS.

Correspondents whose inquiries fail to appear should repeat them. If
not then published, they may conclude that, for good reasons, the
Editor declines them. The address of the writer should always be
given.

Inquiries relating to patents, or to the patentability of inventions,
assignments, etc., will not be published here. All such questions,
when initials only are given, are thrown into the waste basket, as it
would fill half of our paper to print them all; but we generally take
pleasure in answering briefly by mail, if the writer's address is
given.

Hundreds of inqui