204 Mr. Grace Calvert^ on the Infiuence of Science [Feb. 17, 



quantity of moisture, and then rapidly undergo the chemical changes 

 necessary to fit them for producing the black, purple, lilac, red, pink, 

 and chocolate colours, which the madder root will yield immediately 

 in the dyebeck, according to the nature of the mordant previously 

 fixed in the cloth. 



As it is impossit)le, in the brief space of an hour to convey an idea 

 how various colours are produced on prints, I shall confine my remarks 

 to illustrating the interesting fact that abstruse science has brought to 

 light various substances, which have lately proved valuable accessories 

 to the resources of the calico-printer. Thus, Dr. Prout, some thirty 

 or forty years ago, made the curious discovery, that uric acid possessed 

 the property of giving a beautiful red colour, when heated with nitric 

 acid and then brought into contact with ammonia. The substance 

 thus obtained was further examined by Messrs. Liebig and Wohler, 

 in a series of researches which have been considered as amongst the 

 most important ever made in organic chemistry ; and this substance they 

 called Murexide. In the course of these investigations, they also dis- 

 covered a white crystalline substance called Alloxan. For twenty 

 years both these substances were only to be found in the laboratory ; 

 but in 1851 Dr. Saac observed that alloxan, when in contact with the 

 hand, tinged it red. This led him to infer that alloxan might be 

 employed to dye woollens red; and further experiments convinced him 

 that if woollen cloths were prepared with peroxide of tin, passed 

 through a solution of alloxan, and then submitted to a gentle heat, 

 a most beautiful and delicate pink colour resulted. Subsequently 

 murexide was employed and applied successfully by Mr. Depouilly, of 

 Paris, to dyeing wool and silk, and to printing calicos, by the aid of 

 oxide of lead and chloride of mercury as mordants ; but the great 

 obstacle to its extensive use was the difficulty of obtaining uric acid in 

 sufficient quantity for its manufacture. The idea soon occurred to 

 chemists to extract it from guano ; and this is the curious source 

 whence the chief supply of uric acid is obtained,] and which enables 

 Edmund Potter, Esq., and other printers, to produce the colour called 

 Tyrian purple. 



Another example will be found . in the successive scientific dis- 

 coveries which have led to the discovery of the recently popular 

 colour, Mauve. Lichens, which have been the subject of extensive 

 researches on the part of liobiquet, Heeren, Sir Robert Kane, Dr. 

 Schunck, and especially of Dr. Stenhouse, have yielded to those 

 chemists several new and colourless organic substances, which, under the 

 influence of air and ammonia, give rise to most brilliant colours, and 

 amongst these are orchil and litmus. Dr. Stenhouse, in a most 

 elaborate paper, published by the Royal Society in 1 848, pointed out 

 two important facts ; first, that the colour-giving acids could be easily 

 extracted from the weed by macerating it in lime water, from which 

 the colouring matters were easily separated by means of an acid ; and, 

 secondly, the properties of certain colouring acids, which gave M. 

 Manias, of Lyons, the key which enabled him to produce commer- 



