value of various assistants, tartar, oxalic acid, lactic acid,
sulphuric acid, on the fixation of mordants.

The relative value of tannin matters, etc.

Each dyer should make himself a pattern book into which he should
enter his tests, with full particulars as to how they have been
produced at the side.

It is important that a dyer should be able to make comparative
dye-tests to ascertain the relative strength of any two or more
samples of dyes which may be sent to him.

This is not difficult but requires considerable care in carrying out
the various operations involved.

0.5 gramme of each of the samples of dyes should be weighed out and
dissolved in 100 c.c. of water, care being taken that every (p. 216)
portion of the dye is dissolved before any of the solution is used in
making up the dye-vats. Care should be taken that the skeins of yarn
or swatches of cloth are exactly equal in weight, that the same volume
of water is placed in each of the dye-pots, that the same amounts of
sulphate of soda or other dye assistants are added, that the
quantities of dye-stuffs and solutions used are equal, in fact that in
all respects the conditions of dyeing are exactly the same, such in
fact being the vital conditions in making comparative dye-tests of the
actual dyeing strength of several samples of dyes.

After the swatches have been dyed they are rinsed and then dried, when
the depths of shade dyed on them may be compared one with another. To
prevent any mistakes it is well to mark the swatches with one, two,
three or more cuts as may be required.

It is easier to ascertain if two dyes are different in strength of
colour than to ascertain the relative difference between them. There
are two plans available for this purpose; one is a dyeing test, the
other is a colorimetric test made with the solutions of the dyes.

#Dyeing Test.#--This method of ascertaining the relative value of two
dyes as regards strength of colour is carried out as follows. A
preliminary test will show which sample is stronger than the other;
then there is prepared a series of dye-vats, one contains a swatch
with the deepest of the two dyes, which is taken as the standard, the
others with the other dye but containing 2, 5 and 10 per cent. more
dye-stuff, and all these are dyed together, and after drying a
comparison can be made between these and the standard swatch, and a
judgment formed as to the relative strength of the two dyes; a little