208 Notice of some Recent [March 



oxide of manganese, hydrous protoxide of cobalt, acetate of 

 lime, and phosphate of cobalt. The Avignon madder loses 

 its permanence when treated by acid which dissolves the 

 salt of lime. 



M. Robiquet, who along with Colin and Logier has 

 been paying much attention to the subject, although 

 he does not deny the truth of the facts to a certain 

 extent, brought forward by the German chemist, ascribes 

 them to a different cause. He affirms, that lime is not 

 necessary for obtaining permanent madder colours, and 

 indeed, that its presence impedes good dyeing. He has 

 found in madder two colouring matters, alizarine and pur- 

 purine, which vary in their relative proportions, according 

 to the nature of the soil, the cultivation, climate, and age 

 of the root. In most of the acids, alizarine is insoluble, so 

 that when an acid is present, this colour cannot be fixed. 

 The Avignon madder contains no free acid, while the Alsace 

 madder does, as is apparent from its yellow colour. The 

 latter contains much purpurine, and is therefore, better 

 fitted than the Avignon madder, for dyeing lake colours, 

 the agent necessary being purpurine. A hot solution of 

 alum dissolves the purpurine, and does not attack the 

 alizarine, which is remarkable, because, when the latter 

 has once combined with alumina, the affinity is very strong. 

 Robiquet, infers therefore, from these circumstances, that 

 it is not the same colouring matter which becomes alter- 

 nately fixed or fugitive, according to the presence or absence 

 of chalk, but that it is owing to the existence in the madder 

 of two distinct colouring matters, one of which, the purpu- 

 rine is soluble in acids, and can therefore, readily be 

 brought in contact with the mordant, while the other re- 

 quires neutralization, previous to solution. Robiquet found 

 that during boiling, carbonic acid was extracted from mad- 

 der, which he considers as being either present naturally, 

 or as being formed by the alteration of some of the prin- 

 ciples during the process. At a temperature of about 300°, 

 not only carbonic acid, but acetic acid also, without oil was 

 discharged. Robiquet conceives, that the fine colour of 

 Turkey red is owing to the combination of the two colouring 

 matters, and that the fixation of the purpurine is to be 

 ascribed to the oil, ( Ann. de Chim. lvii. 70.) 



