272

DYEING AND CALICO PRINTING.

temperature is raised from 25 0 to go°; afterwards the sample of cotton is firstrinsed in cold and next washed in hot water, dried, and ironed. The samedyeing process as above described can be applied to test the value of extractsof madder, green alizarin, &c., with this understanding—-that not only thequantity of such materials, but also of water, has to be modified. Resinousextracts should be first dissolved in a small quantity of alcohol, whereby thesolution of colouring matter in the bath is promoted. As a general rule, thequantity of water to be employed in the process has to be decreased withincertain limits, according to the higher degree of concentration of the tin&orialsubstance. For instance, with an extra# from sixteen to twenty timesstronger than madder, 250 cubic centimetres—4 litre—- of water is sufficientfor a surface of 25 square centimetres and the proper dose of dye material.

It is easily perceived that the process of test dyeing just described onlyyields results which can be compared with a standard sample, but the utilityof this process is enlarged when dyeing experiments are made with decreasingquantities of the standard sample, the quantity—or rather size—of the cottonremaining the same. It is evident that—starting with 10 grms. of madder,5 grms. of fleur de garance, and i*6 grms. of garancin—a set of dyed samplesmay be produced, the colours of which, before as well as after the aviva^e^will be of less intensity, and we may thus construct a table or scale of colours,taking fleur de garance, for instance, as follows -

No. 1.5*oo grms.

No. 2. 4*50 „

No. 3.4-00 „

No. 4.3*50 „

No. 5.3-00 „

No. 6.2'50 „

and so on ; and when an experimental dyeing result made with 5 grms. offleur happens to be equal to between 2 and 3, we can say that 5 grms. of thatfleur have a tinctorial value of from 4^5 to 4 grms. of the standard sample, oron average = 85, the standard being 100.

As regards the evaluation of the absolute quantity of colouring matterpresent in madder, none of the very large number of methods proposed forthis purpose answer the objed in view. These processes, moreover, are all ofso complicated a nature, and require such a series of manipulations, that theyare of no use whatever for practical work in dye establishments. M. Schlum-berger has devised a method which gives satisfactory approximative results, andis based upon the dissolving power of acetic acid upon the colouring matter.Take 10 grms. of madder, which place in a suitably shaped glass vessel,e.g ., a wide-mouth bottle ; add 500 grms. of distilled water heated to 30°,-andadd a small quantity of beer yeast. Leave the mixture to ferment for twenty-four hours at a suitable temperature ; filter off, and wash with distilled water,acidified with one-fiftieth of its bulk of acetic acid. Instead of the fermenta-tion process, we may steep the madder in water acidified with acetic acid,for some hours, at 30°. Neither this operation nor that of fermentation isnecessary when fleur de garance is to be tested. The residue left on the filteris boiled for ten minutes with a litre of very dilute acetic acid,—sp. gr. 1*005,or about i° Tw.,—and decanted, after some rest pouring, the liquid on a filter,