The _argol_ is professed to be put in to counteract the sulphuric acid of the sulphate of iron; the _alkali_ is said to cause the logwood to retain its natural violet colour: and if too great a quantity of logwood be not used, the result would be as above stated. But the author presumes that such a black would not be at this time much esteemed. We object to the introduction of so much, indeed of any alkali or argol, as the time employed in performing the process is wasted. Alkali is good, however, where a chemic green is to be dyed black. Wool will take up whatever the copper contains necessary to dye black; but, for the beauty of the colour and the durability of the cloth, it is best to let it have most of its ground of vegetable colour before it has the sulphate of iron, which blackens that ground, with sumach instead of galls; and even in some instances, dyeing some goods without the sumach. Were the author, however, to direct the dyeing of black cloth, such as should be of the best kind, he would have _an indigo ground with logwood and alder-bark, without old fustic or oak saw-dust; and to finish the cloth he would use sumach, sulphate of iron, and a small quantity of verdigris. He would give it the blue ground first; then the logwood, alder-bark, and verdigris; and then finish it with sumach and sulphate of iron._ If the blue ground were omitted, he should dye the cloth twice, giving it more of logwood and alder-bark, but verdigris the same; and finish it with sumach and sulphate of iron. Nevertheless, when we dye to a pattern, the pattern must be our guide. Different goods will require different quantities of drugs. Logwood should be about one-fourth of the weight of the goods; the sulphate of iron about one-fifth of the logwood; alder-bark, when used, about the same quantity as sulphate of iron; but for some yarns this bark is not used, nor is it necessary; and where fustic or oak saw-dust is used, there is the less necessity for using alder-bark. The sumach must be about the same quantity as sulphate of iron. Remember that carbon is generally considered as that which makes the richness of a dye. That it is the iron in the sulphate of iron, combined with the tannin and gallic acid which are assumed to be in the sumach and logwood, that produces the blackness of the dye; but this _theory_ is questionable. See _below_. The way to ascertain when the quantities of drugs are most appropriate for producing the desired effect is as follows:— First, ground with different quantities of drugs, from three to five or seven patterns, and use from one third to one fifth of sulphate of iron and sumach to the grounding; afterwards finish with the remainder of the sulphate of iron and sumach: the fuller the ground the richer will be the black, if the logwood be not in excess, and the quantities be used as thus stated.