The next proof consists in boiling a quarter of an ounce of _soap_ in a pint of water, with half a quarter of an ounce of the dyed stuff or thread for five minutes. With this proof all sorts of _yellow_, _green_, _madder-red_, _cinnamon_, and similar colours are to be tried. The proof with _tartar_ consists in boiling one ounce of that salt, previously powdered very fine, with a quarter of an ounce of dyed thread or stuff, in a pint of water for five minutes. This proof is used for all colours bordering upon _fallow_, or _hair-brown_.—_Journal of Science_, vol. xxii. 219. But notwithstanding these general rules may be given for _dye-tests_, yet so many are the niceties in this art, that, after all, nothing but long practice combined with scientific knowledge, will enable the dyer to become in this respect, a complete and successful artist. _On dye-houses and the water proper for dyeing._ The _dye-house_ should be as spacious as possible, according to the quantity of work intended to be done in it; it should be also as near as possible to a clear running stream. The floor should be a mixture of lime and cement, and sufficiently inclining, so that water, the old contents of the vats, &c. &c. may run off freely when thrown down. A dyer cannot be too particular in regard to the _water_ which he uses. Some pump, well, and other spring waters, contain _iron_; this is injurious to many colours, while for black, brown, slates, and grey, it is very advantageous. It has been supposed that some dyers succeed in dyeing even the very same colour in a superior manner, in consequence of the peculiar purity or other properties of the water which they use. To discover whether water contains iron or not, a little tincture of galls or prussiate of potash must be dropped into it; if a purple or blue tinge be produced in the water, we may be assured that it does contain iron. For dyeing delicate colours, the water, which ought to be chosen for such purpose the purest and best, should be heated with bran in a bag, when much of the contents of the water inimical to dyeing will rise to the top in the form of a scum, and should be taken off just before the water boils. Instead of bran, a little alum will answer the same purpose when it is not inimical to the colour intended to be dyed. The boiling point of water is at the degree of 212° of _Fahrenheit's thermometer_; the freezing point is at 32° of the same instrument; blood heat is at 98°. _Miscellaneous observations._