MADDER 169 



lime and other bases contained in the root or added to the dye-bath, and thus permit 

 the liquid to take up fresh quantities from the madder. If the quantity of madder 

 was exactly proportioned to the quantity of fabric to be dyed, then it becomes, in this 

 way, gradually exhausted of all available colouring-matter. The extractive matter at 

 the same time acquires a brown colour by the combined action of the heat and oxygen, 

 and covers the whole surface of the fabric with a uniform brown tinge. When the 

 dyeing is concluded the liquor appears muddy and of a pale dirty-red colour. It still 

 contains a quantity of colouring-matter in a state of combination with lime and other 

 bases from the madder, or with portions of the mordant mechanically detached from 

 the fabric. The residual matter at the bottom of the liquor also contains a quantity 

 of colouring-matter in a similar state of combination. By mixing the residue and 

 the liquor with sulphuric or muriatic acid, boiling, and then washing with water, the 

 various bases are removed, and the colouring-matter is thus made available for dyeing. 

 Occasionally, when a very great depth of colour is required, it is found advisable to 

 let the goods pass through a second dyeing operation, instead of obtaining the requisite 

 shade at once. 



After the calico has been removed from the dye-bath and washed in water, it 

 presents a very unsightly appearance. The alumina-mordant has acquired a dirty 

 brownish-red colour, and the iron-mordant a black- or brownish-purple, according to 

 its strength, whilst the white portions are reddish-brown. In the case of ordinary 

 colours the fabric is now passed through a mixture of boiling bran-and-water, or 

 through a weak solution of chloride of lime, or it is exposed for some time on the grass 

 to the action of air and light, or it is subjected to several of these processes in succes- 

 sion, by which means the impurities adhering to the mordants or the fibre are, in a 

 great measure, either removed or destroyed, the white portions recovering their purity, 

 and the red, black, purple, and chocolate, appearing afterwards sufficiently bright for 

 ordinary purposes. That the colours, however, even after being thus treated, still 

 contain in combination with the mordants other substances in addition to the red 

 colouring-matters, may be proved by a very simple experiment. If a few yards of 

 some calico, which has been treated as just described, be immersed in dilute muriatic 

 acid in the cold, the mordants are removed, and the colours are destroyed ; orange- 

 coloured stains being left on the places where they were before fixed. After washing 

 the calico with cold water, the orange-coloured matter may be dissolved in alkali, and 

 the calico left entirely white. The solution, which is brownish-red, gives, with an 

 excess of acid, a reddish-brown flocculent precipitate. This precipitate, after being 

 collected on a filter and well washed with water, is found to be only partially soluble 

 in boiling alcohol, a brown substance, consisting partly of pectic acid, being left un- 

 dissolved. The yellow alcoholic solution leaves, on spontaneous evaporation, a brown 

 crystalline residue, which is found on examination to contain alizarine, purpurine, a 

 little rubiacine, or some similar compound, and a brown amorphous substance. The 

 removal of these various impurities, associated with the alizarine, seems to be a prin- 

 cipal object of the treatment to which madder-colours are subjected, when it is desired 

 to give them the highest degree of brilliancy of which they are susceptible. This course 

 of treatment, as applied to printed calicoes, may be shortly described as follows : The 

 goods, after being very fully dyed, generally with the addition of chalk, and then 

 washed, are passed for some time through a solution of soap, which is heated to a 

 moderate temperature. By this means a great deal of colour is removed, as may be 

 seen by the red tinge of the soap-liquor, and the purity of the white portions is almost 

 entirely restored. During this process the brown and yellow coloxir ing-matters im- 

 probably removed by double decomposition, the alkali of the soap combining with 

 and dissolving them, while the fat acid takes their place on the fabric. After being 

 washed the goods are passed through a weak solution of acid, mostly sulphuric or 

 oxalic acid, or an acid tin-salt, which causes the colours to assume an orange tinge. 

 The point at which the action of this acid-liquid is to be arrested can only be ascer- 

 tained by practice. The next step in the process is, after washing the goods, to treat 

 them again with soap-liquor, which is gradually raised to the boiling-point, and they 

 are lastly subjected to the action of soap-liquor in a close vessel under pressure. By 

 exposing the goods on the grass for some time after the first soaping, the use of acid 

 may be obviated, but the process then becomes much more tedious. In this way are 

 produced those beautiful pinks and lilacs which, for delicacy of hue, combined with 

 great permanence, are not surpassed by any dyed colours known in the arts. Whether 

 the fat acid of the soap employed forms an essential constituent of these colours is not 

 certainly known, but it is probable that it contributes to their beauty and durability. 

 It is certain, however, that they always contain fat acid. If a piece of calico which has 

 gone through the processes just described be treated with muriatic acid, the colour is 

 destroyed, and a yellow stain is left in its place. This yellow stain disappears on 

 treating the calico, after washing with water, with alkali, yielding a solution of a beau- 



