_Assay._ The SAMPLE is drawn from as near the centre of the cask containing the alkali as possible, and at once placed in a wide-mouthed bottle, which is then closely corked up and numbered. Before proceeding to the assay, the contents of the bottle are thrown on a piece of dry paper, the lumps crushed small, and the whole reduced to coarse powder as rapidly as possible. The number of grains required for the trial are then at once weighed, placed in a phial or small glass tube, and agitated with about 1/2 oz. of hot water. After a short time allowed for repose, the clear liquid is poured off into a beaker-glass or other vessel in which the trial is to be made. This process is repeated with a second and a third quantity of water, or until nothing soluble remains, shown by the last washings not affecting the colour of turmeric paper. The greatest care must here be taken not to waste the smallest portion of the liquid, which would render the results inaccurate. To the solution in the beaker-glass a little solution of litmus is added, unless the acid is tinted with it when it is unnecessary. The solution is now heated until near its boiling point, and a piece of white paper or porcelain put behind it, to better show up the changes of colour. The alkaline solution is now treated with the standard test-acid, which is poured carefully from an alkalimeter or Mohr’s burette, until the solution, after turning a purple red, suddenly assumes a pink colour. Neutralisation being thus effected, the operator allows the sides of the alkalimeter or burette to drain, and then either ‘reads off’ the number of divisions which have been consumed, or (if using the test-acid by weight) determines the quantity by again weighing the alkalimeter. The common practice is to allow two drops (= 1/5th of an alkalimetrical division by VOLUME, or 2 gr. by WEIGHT) for over-saturation, which is, therefore, deducted from the ‘observed quantity’ of the test-liquor employed. In testing solutions of the PURE or CAUSTIC ALKALIES, the colour, on neutralisation, suddenly changes from blue to pink or red, without any intermediate vinous or purple colour being produced. The quantity of test-acid used gives the absolute or per-centage composition of the sample examined, according to the constitution of the test-acid used. _Standard Acids._ The various test-acids in use as described below, each being used by different operators as they think best.