REMARKS ON DYEING. 57 



The bleaching compound, alluded to above, is made " by pass- 

 ing; the gas through slaked lime kept in vessels, in which it is con- 

 stantly agitated by machinery. After it ceases to be absorbed, the 

 product is removed, put into vessels, and kept as much as possible 

 excluded from air." [^Fyfe's Chemistry, 



As the art in question, depends upon the ditferent attractions, 

 which the substances acted upon, have for each other, it is evi- 

 dent, that the Dyer cannot be too cautious in procuring the best 

 materials. It is, undoubtedly, often the case, that he fails to pro- 

 cure a good color, on account of the adulteration of some of the 

 ingredients. It is, therefore, highly necessary, that he be sufficient- 

 ly acquainted with Chemistry, to detect any impurities, and also 

 know how to purify what he tinds to be impure; for instance, 

 alum, a substance which the Dyer catuiot do without, is often con- 

 taminaied with iron. The following method of detecting it, when 

 present, will, therefore, be worth remembering : 



Since the new Tarilf has been established, alum has been made 

 in this country. As some lots tVom each manufactory have been 

 pure and good, whilst other lots, fiom the same factories, have 

 been impure, and calculated to injure the dyer, I have considei'ed 

 it may be advantageous to (he manufacturer, as well as to the dyer, 

 to point out its occasiotial defects, and the mode of testing it, so as 

 to ascertain its injurious impurity. 



Alum is a mordant more generally used than any other, it being 

 necessary to the production of every fine color excepting scarlet. 

 It is a necessary condition to the production of fine colors, that 

 alum should be free from every material which have a tendency to 

 sadden the dye. Iron will do this to a greater degree than any 

 other metallic substance, yet many lots of alum in this market aie 

 suliiciently impregnated with iron to desti-oy every fine color in 

 which it may be used, and this has no doubt been the cause why 

 many of our red flannel dyers have so frequently produced a dull 

 brick color, from the same process, which at other times have ob- 

 tained them brilliant reds. In dying of dark colors, such as greens, 

 browns, dark drabs, olives, clarets, modenas, &c. i:c., the presence 

 of a small portion of iron will not be felt, but in all the finer colors 

 the eiTect is highly destructive. 



According to Vauquelin's analysis, alum should contain 30.52 

 sulphuric acid, 10.50 alumina, 10.40 potash, and 48.50 water of 

 crystallization. Alum is inade either from aluminous schistus, con- 

 taining sullicient sulj>hur to acidiiy, by roasting or exposure, the 

 alumina of the schistus, or from sulphuric acid and clay. When 

 the schistus, or clay, contains iron, a portion of it will be found in 

 the alum when crystallized. The manufacturer to get rid of the 

 iron, should test the liquor before crystallizing, and precipitate it 

 previous to submitting the alum liquor to that process. This j)r(- 

 cautionary measure would elfectually prevent the existence of iron 

 « Vor.. I. 



