Alkaline leys are also to be judged of by their weight compared with that of water; a wine pint of water usually weighs about sixteen ounces avoirdupoise; all alkaline leys are _heavier than water_, and the heavier they are the more alkali they necessarily contain. A wine pint of some of them will weigh more than seventeen ounces. To return to the dyeing of cotton a chemic blue: (to which a knowledge of these chemical processes, as well as of other processes in our work, is essentially necessary,) take some of the blue liquid prepared with indigo and sulphuric acid, as before directed, and put it into a vessel large enough to hold two or three times as much as is intended to be put in, in order that there may be room to stir it; add some of the potash, or alkaline liquor, by degrees till, after several trials, the mixture ceases to be sour; or, if you do not like to taste it, take a small slip of cotton or muslin and dip it in, after having wetted it out in warm water. If the acid be neutralized the cotton will be sound, if not it will be tender _when dried_: if the acid predominates much the cotton will be as rotten as tinder; when the cotton is perfectly strong and sound after being dried, the liquid is in a proper state to dye both cotton and muslin. The goods to be dyed must first be wetted out and wrung, then work them in the flat tub with water, with a little of this blue added, and well stirred in proportion to the shade wanted. From half a pint to a pint of the liquid blue is sufficient for two pieces of twenty-four or twenty-eight yards each, if not of a very full pattern. Blue, when dyed, should be dried in a cool stove, and if book-muslins, framed; furniture should be stiffened, glazed, or calendered. The preceding are essentially the same directions for preparing and dyeing with the _chemic blue_ which were given in the first edition of this work, and which we see no reason to alter. As, however, for _silk_ in particular, another method has been given in the late work of Mr. M'KERNAN, we give his processes below. _Sulphate of Indigo._ "Take one pound of the best flora indigo in very fine powder, put this into a stone-ware or lead vessel, then add gradually three pounds of the best sulphuric acid, specific gravity 1.800; mix well and stir often, and in twenty-four hours the indigo will be dissolved. Adding three ounces of sulphur to the acid, and heating it to 180°; then, when cooled to 100°, pouring the acid off the sediment, and then adding to it the indigo, is considered the best way of opening or dissolving the indigo. When the indigo and acid have been mixed twenty-four hours, add three pints of boiling water; stir often; when cold it will be fit for use." _To neutralize the sulphate of indigo._