and at 95 per cent. (by volume) ought to extract
no color, even if gently warmed (not boiled). Solution of oxalic acid
saturated in the cold, solution of borax, solution of alum at 10 per
cent., and solution of ammonium molybdate at 33-1/3 per cent. ought
not to extract any coloring matter at a boiling heat. The borax
extract, if subsequently treated with hydrochloric acid, should not
turn red, nor become blue on the further addition of ferric chloride.
Solutions of stannous chloride and ferric chloride with the aid of
heat ought entirely to destroy the blue coloring matter. Glacial
acetic acid on repeated boiling should entirely dissolve the coloring
matter. If the acetic extracts are mixed with two volumes of ether and
water is added, so as to separate out the ether, the water should
appear as a slightly blue solution, the main bulk of the indigo
remaining in suspension at the surface of contact of the ethereal and
watery stratum. This acid watery stratum should be colorless, and
should not assume any color if a little strong hydrochloric acid is
allowed to fall into it through the ether. No sulphureted hydrogen
should be evolved on boiling the yarn or cloth in strong hydrochloric
acid. On prolonged boiling, supersaturation with strong potassa in
excess, heating and adding a few drops of chloroform, no isonitrile
should be formed.--_W. Lenz_.

* * * * *

THE SCIENTIFIC AMERICAN

ARCHITECTS AND BUILDERS EDITION.

$2.50 a Year. Single Copies, 25 cts.

This is a Special Edition of the Scientific American, issued
monthly--on the first day of the month. Each number contains about
forty large quarto pages, equal to about two hundred ordinary book
pages, forming, practically, a large and splendid MAGAZINE OF
ARCHITECTURE, richly adorned with _elegant plates in colors_ and with
fine engravings, illustrating the most interesting examples of modern
Architectural Construction and allied subjects.

A special feature is the presentation in each number of a variety of
the latest and best plans for private residences, city and country,
including those of very moderate cost as well as the more expensive.
Drawings in perspective and in color are given, together with full
Plans, Specifications, Costs, Bills of Estimate, and Sheets of
Details.

No other building paper contains so many plans, details, and
specifications regularly presented as the Scientific American.
Hundreds of dwellings have a