A good deal of shoddy is used in making the cheaper class of these goods, and it is quite natural that such "artificial wool" behaves differently from pure wool, not only with regard to its shade resulting from mixing and working together differently dyed waste wools, but also on account of its possessing a greater affinity for all kinds of dye-stuff than raw wool; this in consequence of the carbonisation and washing processes it has undergone, and also of the mordants which the material may retain from previous processes. Therefore (and especially in dyeing light shades on goods manufactured of shoddy) only a small quantity of soda or borax is to be added to the dye-bath and severe boiling is to be avoided. Wherever it is possible goods which are to be dyed in light shades should be made from the palest materials, and the dark qualities only used for goods which are to be dyed in dark shades. This rule can, of course, not always be adhered to. Quite often a light and bright shade is to be dyed on comparatively dark material. This cannot be achieved by simply dyeing it, the goods must be stripped or bleached before dyeing. For this purpose either energetically reacting, oxidising reducing agents are applied. Of the former, bichromate of potassium is principally used. Boil the (p. 175) goods for half to three-quarters of an hour with 3 to 5 per cent. bichromate of potassium, 2 to 4 per cent. oxalic acid, and 3 to 5 per cent. sulphuric acid, wash in a fresh warm bath charged with soda in order to entirely neutralise the acid which has remained in the goods, or else the wool would be dyed too deep a shade. In some cases hydrosulphite has proved a useful reducing agent; it can be easily prepared from ordinary bisulphite of soda in the following manner. Add 10 oz. ammonia (0.9 specific gravity) to a gallon of bisulphite of soda, 32 deg. Tw.; then add slowly under a brisk stirring 10 oz. zinc-dust, and let the entire mixture settle well, using only the clear solution. Treat the goods from fifteen to twenty minutes in a bath of 140 deg. F., to which first add at the boil 3/4 oz. acetic acid, 10 deg. Tw., per gallon water, and then 4 to 6 gallons clear hydrosulphite solution per 100 gallons liquor. Then rinse very well and dye in the usual manner; avoiding, however, too high a temperature. As on this class of goods dark shades are mostly dyed, the goods need only very rarely be stripped. _Bright Yellow_.--Use 2 lb. Thioflavine S in a bath which contains 4 lb. Glauber's salt per 10 gallons of dye-liquor. _Good Yellow_.--A very fine deep shade is dyed with 2-1/2 lb. Diamine Gold, and 24 lb. Diamine Fast Yellow A in the same way as the last. Here advantage is taken of the fact that while the Diamine Gold dyes the wool better than the cotton the Diamine Yellow dyes the cotton the deepest shade, and between the two a uniform shade of yellow is got.