CHEMICAL SCIENCE. 233 



specimens, for which I am likewise indebted to Mr. Nicholson, is most 

 instructive in this respect. Observe, it commences with a large mass 

 of coal, weighing not less than one hundred pounds, ; the bottles 

 which follow contain the coal-tar oil, naphtha, benzole, nitro-benzoi, 

 and aniline, obtainable in succession from one hundred pounds of 

 coal. Remark how they gradually diminish in size, and how small, I 

 might almost say insignificant, appears the bulk of magenta finally 

 obtained. But compare the bulk of wool which this minute quantity 

 will dye. It approximates to the bulk of coal with which we started. 

 This comparison evinces perhaps sufficiently the extraordinary tinc- 

 torial power which this class of dye possesses ; but a very simple 

 experiment may possibly convey to you this idea even in a more 

 impressive manner. The white paper which covers this large frame 

 has been dusted over with a minute quantity of mauve ; a second one 

 is treated in a similar manner with magenta. The quantity of color- 

 ing matter is so small that the paper has retained its original 

 white color; but observe how it changes when I dash a beaker full 

 of spirit against these squares. Immediately the lovely purple of 

 mauve is developed upon one of them, while the other one exhibits 

 the dazzling crimson of magenta. 



As a new art, the manufacture of these colors is of great impor- 

 tance. Hitherto England has been dependent upon foreign countries 

 for its dyes. We have imported madder from Holland, from Turkey, 

 and from France, and blue colors from India, in order to produce our 

 calico prints ; but you see now we are likely to reverse this. We 

 find in this waste product, coal tar, the three primitive colors, out of 

 the mixture of which we can produce almost any shade we desire. 



THE USE OF MORDANTS. 



In order to remove the mordants used in fixing the colors upon 

 printed cottons, 'the calico-printer formerly made use of a curious 

 process, which was, to pass the cloths through baths in which the 

 dung of cow-houses was placed. In this way all the soluble mordants 

 were converted by the cow-refuse into insoluble substances, which 

 could no longer attach themselves to the cloth and cause a confusion 



^3 



of the colors. In consequence of this operation large dairy establish- 

 ments were connected with print-works, so that the printer might 

 have a sufficient quantity of cow-refuse for his purpose. After a 

 time, when the action of this substance began to be properly under- 

 stood, chemists asked themselves whether some substitute could not 

 be used, so that this objectionable process might be dispensed with. 

 They soon discovered that the peculiar action of this refuse upon the 

 mordants was due to the phosphates which it contained to a consid- 

 erable extent ; and it was then easy to make artificial phosphates, 

 phospate of soda and phosphate of lime, and these were mixed 

 together with glue, and sold for a lorn? time under the name of 



c5 ^3 ' 3 



" dung substitute." Within the last few years chemists have found 

 that even these phosphates are not required, and that it is better to 

 use arseniate of soda arsenic acid united with soda. You may 

 have some idea of the enormous quantity of this highly poisonous 

 salt that is used, when in Lancashire alone five hundred tons of this 

 arseniate are annually made for the purposes of the calico-printer. 

 20* 



