DYEING. 



261 



ncy of 



J"ro<*55 carefully covered with its lid, and some thick blankets, 



of Dyeing to prevent it becoming too cold ; though, notwithstand- 



^"""Y" ^ ing every precaution, and the situation of the vat itself, 



the temperature gradually decreases. When it becomes 



too low, its heat must be restored, by drawing off a 



portion of the liquor from the bath, and pouring it back 



boiling hot into the vat 



Effects of 344. When the lime is used either in too great or in 

 ** cat * too small a proportion, it occasions two very troublesome 



icii-Tii'V Ot !_/ 11 



consequences. In the first case, ti.e colour becomes 

 black, the odour is pungent, and the stuff immersed in 

 the bath comes out of a pale grey colour ; in the se- 

 cond, the colour becomes rusty, the matter at the bot- 

 tom is raised up, the smell is fetid, and, in short, a state 

 of putrefaction has commenced. 



34.01. The first state of the vat is corrected by add- 

 ing to die liquor madder, bran, urine, tartar, &c. ; by 

 reheating the bath ; by leaving it at rest without being 

 raked, and by throwing into it a basketful or two of 

 fresh woad. The putrefactive state is corrected by the 

 addition of lime; by frequent raking, &c. 



346. When cloth is to be dyed in a woad vat, the 

 bath is stirred about two hours before the immer- 

 sion of the stuff; and to prevent the latter coming 

 in contact witli the sediment at the bottom of the vat, 

 it is supported by a netting, stretched upon iron or cop- 

 per hoops, which are fastened with cords to hooks on 

 the sides of the vat. When wool is to be dyed, another 

 netting is put over it, to keep it under the surface of 

 the bath. By means of this apparatus, the stuff, pre- 

 viously wrung out of tepid water, is introduced into 

 the vat, and kept there a longer or a shorter time, ac- 

 cording to the degree of strength wished to be given 

 to it. After being taken out, it is wrung above the 

 dyeing vessel, and exposed to the air, when the green 

 colour which it had imbibed in the bath is instantly 

 changed into a blue, by the absorption of the oxygen 

 of the atmosphere. In a rich bath, it is difficult to give 

 an uniform colour to light blues : The best method of 

 obtaining such shades, therefore, is to use vats already 

 exhausted, and which are beginning to grow cold. 



347- That none of the indigo adhering to it may be 

 lost, the stuff is first rinsed in a tub: it is then put 

 through running water, and dried in the shade. When 

 the colour is dull and muddy, the stuff is passed 

 through boiling water, in order* to free it from any ex- 

 traneous impregnation. Stuffs which ore of a very 

 deep blue, ought even to be carefully cleansed by full- 

 ing them with soap, which will tend to equalize the 

 shade without affecting the colour. 



348. A vat in which indigo alone is employed, with- 

 out either pastel or woad, is called an indigo rat. The 

 vessel used in preparing it is a copper, which, being of 

 n conical shape, leaves between it and the surrounding 

 brick-work at the bottom sufficient space for contain- 

 ing the fire. Into this copper are poured about forty 

 buckets of water, (more or less, according to its capa- 

 city,) in which have been boiled six pounds of salt of 

 tartar or potash, twelve ounces of madder, and six 

 pounds of bran. The whole of this mixture, grounds 

 and all, is put into the vat; six pounds of indigo, 

 ground in water, are then to be put in, and, after ra- 

 king it carefully, the vat is to be covered, a slow fire 

 being kept up round it. Twelve hours after it has 

 it is to be raked a second time; and so on 

 every twelve flours, till the liquor becomes blue, which 

 tuppens in al>oiit forty-eight hours. If the bath has 

 been well managed, it will then be of a fine green, co- 

 vered with coppery coloured scales, and a blue scum or 



The theory of the process for preparing this Process^ 

 lie same as for the preceding, the principal dif- *' Dyeing- 



flower. 



bath is the i 



ference consisting in the indigo being dissolved by 



means of an alkali instead of lime. The dyeing process 



is conducted with it in the same manner. 



349. Hellot has described two iudigo vats, in which Two me- 

 the colouring matter is dissolved by means of urine, thodsofpre- 

 A quantity of madder is added to both ; and in the one P a " n S an 

 vinegar, in the other alum and tartar, of each a weight {,"!, H^UOI 

 equal to that of the indigo. The quantity of urine 



must be considerable. Berthollet thinks it probable, 

 that the indigo, deprived of its oxygen by the urine 

 and madder in a state of fermentation, is dissolved by 

 the ammoniac which is formed in the urine, either by 

 the action of the heat, or the putrefactive process. 

 These vats, it must be remarked, are by no means com- 

 parable with that of pastel, or that of indigo already 

 described, much less work being expedited by them, 

 so that they are adapted only to small dye-houses. 



350. Another preparation for dyeing blue with in- Sulphate of 

 digo is obtained by dissolving it in sulphuric acid. The indigo, or 

 resulting compound, which we shall call the sulphate Saxon blut ' 

 of indigo, was first applied to the purposes of dyeing 



at Grossehayn in Saxony, and hence the dye which it 

 affords is usually known by the name of Saxon blue. 

 It is also sometimes called the chemical blue ofPcerner. 



351. Bergman made many experiments, with the Bergman's 



view of ascertaining the best method of dissolving in- P 10 ?* 55 * or 

 T i L i i i v .1 . dyeing Sax- 



digo in sulphuric acid, and applying it in that state as b j^ e 



a dye. From these he concluded, that if the sulphate 

 of indigo has hitherto afforded a dye of little perma- 

 nency, it was entirely owing to the acid being used in 

 too diluted a state. He accordingly used the sulphuric 

 acid in a very concentrated state, putting one part of 

 indigo. fiiH-ly powdered, into eight parts of the acid, of 

 the specific gravity 1.9. The mixture was made in :t 

 glass vessel slightly stopped, and was accompanied 

 with a considerable heat. After a digestion of twenty- 

 four hours in a heat of 30 or 40 degrees, (from 86 to 

 lot- of Fahrenheit,) the indigo was dissolved, and form- 

 ed an opaque black solution. By the gradual addition 

 of water, the intensity of colour was reduced, and ex- 

 hibited in succession every shade of blue. In several 

 experiments described by that illustrious chemist, he 

 kept the stuff to be dyed twenty-four hours in boiling 

 water, and then put a given weight of it into the bath, 

 more or less strong, till the colour of the bath was ex- 

 hausted. From these experiments he ascertained, that 

 one part of indigo would, in this way, produce a deep 

 blue on two hundred and sixty parts of stuff, which 

 appeared to be then saturated with the colouring mat- 

 ter. 



852. This blue penetrates into stuffs with difficulty; Process of 

 and in order to obviate this inconvenience, Quatremere Quatrctnerc 

 and Fa'rner have recommended an addition of potash 

 to the acid. The alkali renders the colour more lively, 

 full, and penetrating. Po-rner directs, in the process 

 which he has prescribed for preparing Saxon blue, four 

 parts of sulphuric acid to one of indigo reduced to a 

 fine powder. The mixture is to be stirred for some- 

 time. After having stood twenty-four hours, one part 

 of good dry potash in fine powder is added ; the whole 

 in well stirred, and, having stood twenty-four 

 hours longer, more 'or less water is gradually added. 

 Instead of potash, Dr Bancroft has used clean chalk, Of Dr Bani 

 and sometimes even in such quantities as to saturate 

 the acid. The indigo was then precipitated with the 

 chalk, and being collected in a solid mass, it was found 

 to be still capable of dyeing a blue on wool, though it 



