DYEING. 



231 



Adjective 

 Colouring 



.Vr.--.T-. 



151. Fustic, the wood of the morns tinctoria, a tree 

 of considerable size, which grows in various parts of 

 the West Indies, affords a yellow colouring matter, 

 which is very extensively used in dyeing. The colour 

 which it yields is neither high nor bright, but it pos- 

 sesses considerable durability, and is less affected by 

 acids than the quercitron and weld yellows. Fustic 

 abounds much in colouring particles, though in this re- 

 spect it is greatly inferior to quercitron, as it only affords 

 one-fourth the quantity of colouring matter. 



152. A strong decoction of fustic i.s of deep red- 

 dish yellow colour, whi;-'.i becomes an orange yellow 

 when diluted with water. The greater number of the 

 acids render this liquor turLid ; a small quantity of a 

 greenish yellow precipitate is formed, and the superna- 

 tant liquor is of a pile yei'ow. Alkalies redissolve the 

 precipitate, and give the liquor a deep reddisli colour. 

 Alum forms a small precipitate of a yellow colour ; 

 alum and tartar a like precipitate. Muriate of soda 

 makes the liquor a little m.>re deeply col, ure 1, with- 

 out producing any precipitate. Sulphate oi' iruii forms 

 a precipitate, which is at first yellow, but afterwards be- 

 comes more and more brown. Sulphate yields a copi- 

 ous brownish yellow precipitate. Fustic and weld are 

 sometimes used together, in quantities proportioned to 

 the desired effect. Fustic is also very commonly em- 

 ployed with the sulphate of indigo, in dyeing Saxon 

 greens upon cloth. 



153. Fustic, as well as many other woods which 

 yield a yellow colour, contains a quantity of resinous 

 and extractive matter in combination with a portion of 

 tannin. This last principle diminishes the brilliancy of 

 the yellow afforded by fustic ; but Chaptal has proposed 

 an easy method of detaching it from the colouring mat- 

 ter, though it may affect its durability. The method 

 to which we allude, i.s founded upon the attraction of 

 tannin for glue. He accordingly recommends that ani- 

 mal substances, containing gelatinous matter, such as 

 bits of leather, glue, &c. should be added to the decoc- 

 tions of fustic. Thi .-; process precipitates the tannin, and 



les the colour to exhibit greater brilliancy. 



1 ."i I . Venice sumach, the wood of the r/iut cotintis, a 

 shrub growing principally in Italy, and the South of 

 France, affords a full high yellow of little durability. 

 Dr Bancroft, indeed, mentions that this defect may, in' 

 a great degree, be remedied, by employing tartar, along 

 with the muriate of tin, the mordant by means of which 

 this colouring matter is usually fixed. Four pounds of 

 the rims cot in us chipped, afford no more colour than one 

 pound of quercitron. It is frequently nixed with other 

 colouring substances, particularly cochineal, to give a 

 fine colour to scarlet ; also for pomegranates, oranges, 

 jonquilles, gold colours, buffs, and in general for all those 

 colours which it is wished should have an orange cast 



15J. Common sumach, (;//< cnriaria,) a shrub, 

 growing naturally in Syria, Palestine. Spain, Portugal, 

 and some parts of N'orth America, yields a |>ale yellow 

 dye, with the aluminous basis. The infusion, wmdh is 

 obtained from the wood previously reduced to powder 

 by a mill, is of a greenish fawn colour, but it soon be- 

 comes brown by exposure to the air. 



156. A solution of potash produces very little change 

 on it, while recent ; acids brighten its colour, and turn 

 it yellow. A solution of alum renders it turbid, and 

 produces a small yellow precipitate. Of all astringents, 

 sumach bears the greatest resemblance to galls. The 

 precipitate which it produces with solutions of iron is 



Adjective 

 Colouring 

 Matters.' 



less in quantity than what is obtained ,by an equal 

 weight of galls, but it is very copious, and may be sub- 

 stituted for them by increasing the quantity. 



157. Sumach alone gives a fawn colour inclining to 

 green ; but cotton stuffs, which have been impregnated 

 with the acetate of alumine, take from it a very good 

 durable yellow. It is principally employed for drab 

 and dove colours in calico printing, and for dyeing black 

 with iron, and the solutions of that metal. 



158. The berries of the rhamnus infcctorius give a Rhamrmi 

 lively yellow, but one which is destitute of durability, infectotiu*. 

 They are chiefly used for topical dyeing, in calico 

 printing. The colour which they communicate is so 



very fugitive, that the practice of dyeing from them 

 should be abandoned. 



159. Saw-wort, serratula tinctoria, affords a better Sanr-won. 

 dye, and may be used as a substitute for weld with the 

 aluminous basis. It yields a bright lemon yellow of 

 considerable permanency, which may be heightened 



with the nitromuriate of tin and tartar. 



CHAP. IV. 



Of the Durability of Colours. 



1 60. In the view which we have hitherto taken of Durability 

 colouring matters, we have considered the mechanical of colours. 

 methods by which they are separated from the sub- 

 stances with which they exist in a state of combina- 

 tion, and the general appearances which they exhibit 

 with a variety of chemical agents. In describing these 

 appearances, we treated them rather as modifications 

 produced upon the original colouring matters, than as 

 actual changes effected in their composition. It must 

 be evident, however, that, from the nature of the che- 

 mical agents to which, in some instances, the colour- 

 ing matters were submitted, decompositions must have 

 taken place, and new compounds been formed; and 

 that these compounds must be more or less durable in 

 proportion as they are capable of resisting the action of 

 the substances to which they are afterwards to be most 

 frequently exposed, viz. light, air, water, acids, alka- 

 lies, and soap. 



161. The influence of light upon colouring matter* 

 has been long known ; but it was reserved for the deli- 

 cate precision of modern analysis to discover the mode 

 of its operation. To do this, a knowledge of the com- 

 position of light itself, the most subtile of all material 

 substances, was no less necessary than an acquaintance 

 with the constitution of coloured bodies. Without en- 

 tering into any detail on this subject, it will be sufficient 

 to state the results which have b:?en obtained by ex- 

 periment. 



162. Light appears to consist of three kind of rays, 



, . i_ /. % . . \ 



which form one homogeneous compound in the solar 

 beam. These have been terjned calorific, colorific, and zing rays 

 deoxidizing rays : (See CIIEMISTHY, p. 32.) It is the on colours. 

 nature of the latter which we propose to consider more 

 particularly at present. The deoxidizing rays exert 

 their agency chiefly in occasioning decomposition. The 

 element which they most frequently detach from a 

 state of combination with other bodies, is oxygen ; and 

 from this property, indeed, they derive their name. 

 Colourless nitric acid exposed to the rays of the sun 

 soon becomes red and fuming, a state which is known 

 to proceed from a partial separation of its oxygen. Oxy- 

 muriatic * acid gas is also decomposed by it, and it* 



^. 



cSi of 



The influence of light in evolving oxygen u equally demonstrated by this experiment, whether we retain the old opinion respecting this 

 ga, or adopt the hypothcei* of Sir Humphry Davy. 



