162 MADDER 



sisted in placing a small quantity of each sample on a slate, pressing the heaps flat with 

 some hard body, and then taking them to a cellar or other damp place. After 10 or 

 1 2 hours they were examined, and that which had acquired the deepest colour, and 

 increased the most in volume was considered the best. This method led, however, to so 

 many frauds on the part of the dealer, for the purpose of producing the desired effect, 

 that it is no longer resorted to. Madder is sometimes adulterated with sand, clay, 

 brick-dust, ochre, sawdust, bran, oak-bark, logwood and other dye-woods, sumac and 

 quercitron bark. Some of these additions are difficult to detect. Such as contain 

 tannin may be discovered by the usual tests, since madder contains naturally no tannin. 

 If the material used for adulteration be of mineral nature, its presence may be dis- 

 covered by incinerating a weighed quantity of the sample. If the quantity of ash which 

 is left exceeds 10 per cent, of the material employed, adulteration may be suspected. 

 The ash obtained by incinerating pure madder consists of the carbonates, sulphates, 

 and phosphates of potash and soda, chloride of potassium, carbonate and phosphate of 

 lime, phosphate of magnesia, oxide of iron and silica. If a considerable amount of 

 any other mineral constituents is found, it is certainly due to adulteration. 



There is probably no subject connected with the art of dyeing which has given rise to 

 so much discussion as the composition of madder, and the chemical nature of the 

 colouring matters to which it owes its valuable properties. The subject has engaged 

 the attention of a number of chemists, whose labours, extending over a lengthened 

 period, have thrown considerable light on it. Nevertheless, the conclusions at 

 which they have severally arrived do not perfectly agree with one another, nor with 

 the views entertained by the most intelligent of those practically engaged in madder 

 dyeing. The older investigators supposed that madder contained two colouring 

 matters, one of which was tawny, and the other red. Kobiquet was the first chemist 

 who asserted that it contained two distinct red colouring matters, both of which 

 contributed to the production of the dyes for which madder is employed ; and his 

 views, though they were at the time of their promulgation strongly objected to 

 by some of the most eminent French dyers and calico-printers, still offer probably 

 the best means of explaining some of the phenomena occurring during the process of 

 madder dyeing. The two red colouring matters discovered by Robiquet were named 

 by him Alizarine and Purpurine, and these names they still retain. Several crystal- 

 lised yellow colouring matters have been discovered by other chemists ; but the only 

 one which exists ready-formed in the madder of commerce is the Bubiacine of Schunck, 

 and this substance may also be taken as the type of the whole class, the members of 

 which possess very similar properties. Among the other organic substances obtained 

 by different chemists from madder, two resinous colouring matters, sugar, a bitter 

 principle, a peculiar extractive matter, pectin, a fermentative nitrogenous substance, 

 and malic, citric, and oxalic acids, may be mentioned. 



When madder is extracted with boiling water, a dark brown muddy liquid, having 

 a taste between bitter and sweet, is obtained. On adding a small quantity of an acid 

 to this liquid, a dark brown precipitate is produced, while the supernatant liquid 

 becomes clear, and now appears of a bright yellow colour. The precipitate consists 

 of alizarine, purpurine, rubiacine, the two resinous colouring matters, pectic acid, 

 oxidised extractive matter, and a peculiar nitrogenous substance. The liquid filtered 

 from this precipitate contains the bitter principle and the extractive matter of madder, 

 as well as sugar and salts of potash, lime, and magnesia. No starch, gum, or tannin 

 can be detected in the watery extract. After the madder has been completely ex- 

 hausted with boiling water, it appears of a dull red colour. It still contains a quan- 

 tity of colouring matter, which cannot, however, be extracted with hot water, or 

 even alkalis, since it exists in a state of combination with lime and other bases, 

 forming compounds which are insoluble in those menstrua. If, however, the residue 

 be treated with boiling dilute muriatic acid, the latter dissolves a quantity of lime, 

 magnesia, alumina, and peroxide of iron, as well as some phosphate and oxalate of 

 lime, which may be discovered in the filtered liquid ; and if the remainder, after being 

 well washed, be treated with caustic alkali, a dark red liquid is obtained, which gives 

 with acids a dark reddish-brown precipitate consisting of alizarine, purpurine. rubia- 

 cine, resin, and pectic acid. That portion of the madder left after treatment with hot 

 water, acids, and alkalis, consists almost entirely of woody fibre. 



A short description of some of the substances just mentioned will not be out of 

 place here, as it may assist in rendering the process of dyeing with madder more 

 intelligible. 



The most important of these substances is alizarine, since it forms the basis of all 

 the finer and more permanent dyes produced by madder. The inatiere colorants rouge 

 of Persoz and the madder-red of Rungo also consist essentially of alizarine, mixed 

 with some impurities. Robiquet first obtained it in the form of a crystalline sublimate, 

 by extracting madder with cold water, allowing the liquid to gelatinise, treating the 



