128 
ON MADDER. 
into little glass globes with 40 parts of water, and 6 parts 
of very pure alum, boiled for a quarter of an hour, and the 
boiling liquids filtered. The grounds are washed with 2 
parts of hot water. Two other decoctions, similar to the 
first, are made, and each time the residue is washed with 2 
parts of hot water. The products of the three decoctions 
are combined, and the liquids from the two samples of 
madder compared by the colorimeter. 
Without doubt this examination with the colorimeter is 
not sufficiently accurate, but it affords valuable indications, 
which, joined to those resulting from the following tests, 
enable us to give a decided opinion. 
2. Determination of the Tinctorial Power by Dyeing. — 
In order to estimate the value of a madder by dyeing, a 
madder of superior quality must be taken as a type of com- 
parison, with which skeins or mordanted calicoes have been 
already dyed, by acting with determinate quantities of pow- 
der, tissue and water. Patterns for comparison should be 
prepared in the following manner : — 
Calicoes are selected, mordanted for red and black, and 
well-cleansed in a dung-bath. They are divided into pieces 
5 centimetres square, and are dyed with proportions of mad- 
der increasing progressively from 1 grm. up to 10 grms., so 
as to have a scale of 10 shades, of which the gradations re- 
present each a known weight of madder. The garancing 
of these pieces is practised in the following manner: — In a 
great copper basin, with a flat bottom, which is covered 
with a layer of hay, are placed three or four glass jars with 
wide mouths, containing from lh litre to 2 litres. The basin 
is filled with ordinary water heated to 104° ; then into each 
of the glass jars the piece of mordanted calico is introduced, 
the madder weighed with care, and lastly, three-fourths of 
a litre of distilled water heated to a temperature of 104°. 
A thermometer is inserted in the water-bath, which is heated 
slow enough for the water not to reach 167° until after an 
hour and a half, avoiding carefully alternations of tempera- 
