Of such chemicals as soda, caustic soda, sodium sulphate (Glauber's salt), tartar, bichromate of potash, it will be found convenient to prepare stock solutions of known strength, say 50 grams per litre, and then by means of a pipette any required quantity can be conveniently added. The same plan might be followed in the case of dyes which are constantly in use, in this case, 5 grams per litre will be found strong enough. Supposing it is desired to make a test of a sample of direct red, using the following proportions: 2 per cent. dye-stuff, 3 per cent. soda, 15 per cent. Glauber's salt, and the weight of the swatch which is being used is 5 grams. The following calculations are to be made to give the quantities of the ingredients required. For the dye-stuff:-- 5 (weight of swatch) multiplied by 2 (per cent. of dye) and divided by 100 equals-- 5 x 2 ------- = 0.1 gram dye 100 For the soda we have similarly:-- 5 x 3 ------- = 0.15 gram soda. 100 For the Glauber's salt:-- 5 x 15 -------- = 0.75 gram Glauber's salt. 100 These quantities may be weighed out and added to the dye-bath, or if solutions are kept, a calculation can be made as to the number of cubic centimetres which contain the above quantities, and these measured out and added to the dye-bath. When all is ready, the bath is heated up, the swatch entered, and the work of the test entered upon. Students are recommended to make experiments on such points as:-- The shades obtained by using various proportions of dye-stuffs. The influence of various assistants--common salt, soda, Glauber's salt, borax, phosphate of soda--in the bath. The influence of varying proportions of mordants on the shade of dyeing. The value of various assistants, tartar, oxalic acid, lactic acid, sulphuric acid, on the fixation of mordants. The relative value of different tannin matters, etc. Each dyer should make himself a pattern-book into which he should enter his tests, with full particulars as to how they have been produced at the side. It is important that a dyer should be able to make comparative dye tests to ascertain the relative strength of any two, or more samples of dyes which may be sent to him. This is not difficult, but requires considerable care in carrying out the various operations involved.