MADDER 167 



trace of colour-producing substance can be detected, either in the liquor or the residual 

 madder, after the operation of dyeing is concluded. The presence of oxygon does not 

 seem to be essential during this process of decomposition, as Decaisne supposed. 

 Nevertheless, according to Schunck, rubian does in reality suffer a partial oxida- 

 tion when its watery solution, mixed with some alkali or alkaline earth, is exposed to 

 the action of the atmosphere, giving rise to a peculiar acid, called by him rubianic 

 acid. When rubian is heated dt a temperature considerably exceeding 212 Fahr., it 

 is converted without much change of appearance into a substance which yields by 

 decomposition resinous colouring-matters in the place of alizarine. The great excess 

 of these colouring-matters contained in the madder of commerce arises, therefore, 

 most probably from the high temperature employed in drying the root. 



Employment of Madder in Dyeing. After the account which has just been given of 

 the composition of madder, it may easily be conceived that the chemical and physical 

 phenomena which occur during the various processes of madder-dyeing, are of a rather 

 complicated nature, and that many of these phenomena have not yet received a per- 

 fectly satisfactory explanation. Nevertheless, the present state of our knowledge on 

 this subject may enable us to give a co.nsistent explanation of the facts presented to 

 us by the experience of the dyer, and even to indicate what direction our labours must 

 take if we wish to improve this branch of the arts. 



In order to produce perfectly-fast colours in madder-dyeing, it is necessary that the 

 madder should contain a large proportion of carbonate of lime, and if the madder is 

 naturally deficient in that salt, the deficiency may be supplied either by using cal- 

 careous water in dyeing, or by adding a quantity of ground chalk. If madder be 

 treated with dilute sulphuric or muriatic acid, so as to dissolve all the lime contained 

 in it, and then washed with cold water until the excess of acid is removed, its tinc- 

 torial power will be found to be very much diminished, but may be entirely restored, 

 and even increased, by the addition of a proper quantity of lime-water or chalk. 

 Hence, too, Avignon madder, which is grown in a highly-calcareous soil, and contains 

 so much carbonate of lime as to effervesce with acids, affords the most permanent 

 colours ; whilst Alsace madder requires the addition of carbonate of lime in order to 

 produce the same effect. This fact was first pointed out by Hausmann, who, after 

 having produced very fine reds at Eouen, encountered the greatest obstacles in dyeing 

 the same reds at Logelbaoh, near Colmar, where he went to live. Numerous trials, 

 undertaken with the view of obtaining the same success in his new establishment, 

 proved that the cause of his favourable results at Rouen existed in the water, which 

 contained carbonate of lime in solution, whilst the water of Logelbach was nearly 

 pure. He then tried a factitious calcareous water by adding chalk to his dye-bath. 

 Having obtained the most satisfactory results, he was not long in producing here as 

 beautiful and as solid reds as he had done at Eouen. This simple fact led to the pro- 

 duction of a series of lengthy Memoirs on the part of some of the French chemists and 

 calico-printers, which fully confirmed the results of Hausmann, without, however, 

 leading to a satisfactory explanation of them. The experiments of Eobiquet prove 

 that in dyeing with pure alizarine the least addition of lime is rather injurious than 

 otherwise, as it merely weakens the colours without adding to their durability. Hence 

 the beneficial effect of lime can only be accounted for by some action which it exerts 

 on other constituents of the root. Bartholdi imagined that this action consisted 

 simply in the decomposition of the sulphate of magnesia, which he found to be con- 

 tained in ordinary madder. It was asserted by others that the carbonate of lime 

 served to neutralise some free acid, supposed by Kuhlmann to be malic acid, which 

 was present in some madders, and which not only to a great degree prevented the 

 colouring-matters from dissolving in the dye-bath, but also combined with the mor- 

 dants to the exclusion of the latter. Though later researches have failed to detect 

 the existence of malic acid in madder, still it is certain that all watery extracts of 

 madder contain pectic acid, which probably exists in the root originally as pectine ; 

 and that this acid, when in a free state, acts most injuriously in dyeing with alizarine, 

 but ceases to do so as soon as it is combined with lime. Nevertheless, it seems that 

 madder which is naturally deficient in lime, cannot be made to replace entirely such 

 madder as has been grown in a calcareous soil, however groat an excess of chalk be 

 used in dyeing. Hence Eobiquet was led to the conclusion that the inferior kinds of 

 madder, which are also the most deficient in lime, contain more purpurine and less 

 alizarine than the superior kinds, and that the carbonate of lime serves partly to 

 combine with the purpurine, and prevent it from uniting with the mordants, and thus 

 producing less permanent dyes. The experiments of Schunck have proved that not 

 only pectic acid, but also rubiacine and the resinous colouring-matters of madder, act 

 detrimentally in dyeing with pure alizarine, by deteriorating the colours and sullying 

 the white parts of the fabric, and that these effects are entirely neutralised by the 

 addition of a little lime-water to the dye-bath. If in dyeing with madder the whole 



