of bichromate of potash is 3 per cent. of the weight of the cloth.  The requisite number of pieces (equal to the number of samples to be tested) should be thoroughly scoured and then heated in the bichromate solution at or near the boiling point for not less than 11/2 hours, after which they should be well washed and then dyed separately in the solutions of equal weights of the extracts at the same temperature and for the same length of time; 15 grains of extract is a suitable quantity for a first trial under these conditions.  These trials can then be repeated with different relative proportions of extract in order to ascertain what weight of a sample would give the same depth of color as 15 grains of the standard example.  Many precautions are required both in the mordanting and dyeing processes in order to obtain trustworthy results; and though the trials with bichromate of potash give the most reliable information of any single test, they should be supplemented by the subsidiary tests already alluded to, and also by a chemical examination, in order to obtain a knowledge, not merely of the wood strength, but also of the general nature of the extract.  An adulteration with molasses or glucose can be best determined by fermentation in comparison with a pure sample.  Mineral adulterants may, of course, be detected by an estimation and analysis of the ash, after making due allowances for variations due to differences in different kinds of the same dyewoods.  The estimation of the individual coloring matters in these extracts by means of a chemical analysis is under all circumstances a task requiring much experience, especially as the coloring principles are associated in different qualities of each class of dyewood with different proportions of other constituents which often give much trouble to the unpracticed experimenter.  Extracts made from logwood roots are now largely manufactured and often substituted or mixed with the extracts of real logwood, and have in some instances been palmed of as logwood extracts of high quality.  The correct determination of such admixtures, like the fixing of anything like the exact commercial value of dyewood extracts, requires nothing less than a complete chemical investigation coupled with numerous dyeing trials in comparison with standard preparations, and should be left to an expert.

The presence in dyewood extracts of coloring matters in various stages of development has hitherto militated against their use in place of the raw materials by many dyers and printers who are still employing inherited and antiquated processes in which the whole of the coloring matter is not rendered available.  It is often asserted by these that even the best of extracts fail to give anything like the results attained by the use of well-prepared woods, and that, indeed, their application proves a complete failure.  Such failure, however, is simply due to the want of chemical knowledge on the part of the dyers, for there is no real difficulty