For the acid we have similarly (5 x 3) / 100 = 0.15 gramme of (p. 215) acid. For the Glauber's salt (5 x 15) / 100 = 0.75 gramme of Glauber's salt. 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 put in 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 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. 0.5 gramme of each of the samples of dyes should be weighed out and dissolved in 100 c.c. of water, care being taken that every (p. 216) portion of the dye is dissolved before any of the solution is used in making up the dye-vats. Care should be taken that the skeins of yarn or swatches of cloth are exactly equal in weight, that the same volume of water is placed in each of the dye-pots, that the same amounts of sulphate of soda or other dye assistants are added, that the quantities of dye-stuffs and solutions used are equal, in fact that in all respects the conditions of dyeing are exactly the same, such in fact being the vital conditions in making comparative dye-tests of the actual dyeing strength of several samples of dyes. After the swatches have been dyed they are rinsed and then dried, when the depths of shade dyed on them may be compared one with another. To prevent any mistakes it is well to mark the swatches with one, two, three or more cuts as may be required. It is easier to ascertain if two dyes are different in strength of colour than to ascertain the relative difference between them. There are two plans available for this purpose; one is a dyeing test, the other is a colorimetric test made with the solutions of the dyes.