20 



(Ol.OlRING M.V1TI:K and Pr.INCIPI.KS OF DYING. 



qual. On ihe other hand, if the affinity 

 between the colouring matter, and the 

 solvent be too great, compared with that 

 between the colouring matter and the 

 cloth, the ciotli will either not take the 

 colour at all, or it will take it very slowly 

 and very faintly. 



Wool has the strongest affinity for al- 

 most all colouring matters, silk the next 

 strongest, cotton a considerably weaker 

 affinity, and linen the weakest affinity of 

 all. 



In order, therefore, to dye cotton, or 

 linen, the dye-stuff should in many cases 

 be dissolved in substances for which it has 

 a weaker affinity than for the solvent em- 

 ployed in the dying of wool or silk. Thus 

 we may use oxide of Iron dissolved in sul- 

 ])huric acid, in order to dye woof: but for 

 cotton or linen, it is better to dissolve it in 

 acetous acid. Were it possible to procure 

 a sufficient number of colouring mitters, 

 having a strong affinity for cloth to an- 

 swer all the purposes of dying, that art 

 would be exceedingly simple and easy. 

 But this is by no means the case; if we 

 except indigo, the dyer is scarcely pos- 

 sessed of a dye-stufT which yields of it- 

 self a good colour, sufficiently permanent 

 to deserve the name of a d3'e. 



This difficulty, which at first sight ap- 

 pears insurmountable has been obviated 

 by a very ingenious contrivance. Some 

 subsiance is employed which has a strong 

 affinity both for the cloth and the colour- 

 ing matter. This sub-stance is previously 

 combined with the cloth which is then 

 dipped in tbesolulion containing the dye- 

 stuff. The dye-stuff combines with the 

 intermetliate substance, which being firm- 

 ly combined with the cloth secures the 

 permanence of the dye. Substances em- 

 ployed for this purpose are denominated 

 mordants. The most important part of 

 dying is undoubtedly the proper choice, 

 and proper application of mordants; as up- 

 on them, the permanency of almost every 

 dye depends. Every thing whieli has 

 been said respecting the npplic:Uion of 

 colourinj5 matters applies equally to the 

 application of mordants. 'Ihey must be 

 previously dissolved in some liquid, which 

 has a weaker affinity for them than the 

 cloth has, to which they are to be applied; 

 and the cloth must be dipped; or even 

 steeped in this solution, in order to be 



saturated with the mordant. Almost the 

 only subsiance used as mordants are 

 earths, metalic oxides, tan and oil. Of ear- 

 thy morxlants the most important and most 

 genei'ally used, is alumina.lt is used either 

 in the state of common alum, in which 

 it is combined wiih sulphuric acid or in 

 that of acetate of alumina. Alum when 

 used as a mordant, is dissolved in water, 

 and very fr-equently a quantity of tartar 

 is dissolved along with it. 



Into this solution the cloth is put, and 

 kept in it till it has absorbed as much al- 

 umina as is necessary. It is then taken 

 out, and for the most part washed and 

 dried. It is now a good deal heavier than 

 it was befor-e, owing to the alumina which 

 has combined with it. The tartar serves 

 two purposes; the potass which it contains 

 combines with the sulphuric acid of the 

 alum, and thus prevents that very corro- 

 sive substance fr-om injuring the texture 

 of the cloth, which otherwise might hap- 

 pen, the tartarous acid on the other hand, 

 combines with part of the alumina and 

 forms a tartrate of alumina which is more 

 easily decomposed by the cloth than alum. 

 Acetate of aluinina has also been used in 

 dying. This mordant is now prepared 

 by pouring acetate of lead into a solution 

 of alum; a dou!>le decomposition takes 

 place, the sulphurous acid combines with 

 the lead, and the compound precipitates, 

 in the form of an insoluble powder, while 

 the alumina combines wiih the acetous 

 acid, and remains dissolved in the liquid. 

 I'his mordant is employed for cotton and 

 linen, which have a weaker affinity than 

 wool for alumina. It answers much bet- 

 ter than alum; Ihe cloth is much easier 

 satur-ated with alumina and takes in con- 

 sequence, both a richer and more perma- 

 nent colour. 



( To be continued.) 



BEETS INTO 



PROCESS OP CONVERTING 

 SUGAR. 

 iiaiTuel's Method. 



\sl. proces.^. To wash the roots and 

 cut off the topi. 



2. To reduce the root to a pulp, this 

 may be done in various ways; two indent- 

 ed cylinder's, one working within the 

 other is considered the best. 



3. To express the juice. This should 

 be done as speedily as possible, for the 



