on.

The cupra-ammonium solutions of cellulose are by no means stable but
change on keeping. When freshly prepared, the cellulose may be
precipitated from them almost unchanged by the addition of such bodies
as alcohol, sugar and solutions of neutral alkaline salts. On keeping
the cellulose undergoes more or less hydrolysis or even oxidation, for
it has been observed that oxycellulose is formed on prolonged digestion
of cellulose with cupra-ammonium solutions, while there is formed a
fairly large proportion of a nitrite.

On adding lead acetate to the cupra-ammonium solution of cellulose, a
compound of lead oxide and cellulose of somewhat variable composition is
precipitated. It is of interest also to note that on adding metallic
zinc to the cupra-ammonium solution the copper is thrown out and a
solution containing zinc is obtained.

This action of cupra-ammonium solutions on cellulose has been made the
basis for the production of the "Willesden" waterproof cloths. Cotton
cloths or paper are passed through these solutions of various degrees of
strength according to requirements, they are then passed through rollers
which causes the surface to become more compact. There is formed on the
surface of the goods a deposit of a gelatinous nature which makes the
surface more compact, and the fabric becomes waterproof in character
while the copper imparts to them a green colour and acts as a
preservative. The "Willesden" fabrics have been found very useful for a
variety of purposes.

CHAPTER II.

SCOURING AND BLEACHING OF COTTON.

Preparatory to the actual dyeing operations, it is necessary to treat
cotton in any condition--loose cotton, yarn, or piece--so that the
dyeing shall be properly done. Raw cotton contains many impurities,
mechanical and otherwise; cotton yarns accumulate dirt and impurities of
various kinds during the various spinning operations, while in weaving a
piece of cotton cloth it is practically impossible to keep it clean and
free from dirt, etc. Before the cotton can be dyed a perfectly level and
uniform shade, free from dark spots or light patches, these impurities
must be removed, and therefore the cotton is subjected to various
scouring or cleansing operations with the object of effecting this end.
Then again cotton naturally, especially Egyptian cotton, contains a
small quantity of a brown colouring matter, and this would interfere
with the purity of any pale tints of blue, rose, yellow, g