Exhaustion.--10 _grm._ of valonia, 20-30 _grm._ of bark, or corresponding quantities of other material, are boiled briskly for half an hour with 1 _litre_ of distilled water, a funnel being placed in the neck of the flask, and great care being taken at first to avoid frothing and boiling over. The flasks used should have a capacity of at least 1-1/2 _litre_. The whole contents are finally rinsed into a gauged flask, allowed to cool to 59° F. (15° C.), and made up to 1 _litre_. In the case of sumach, a little more boiling even than this is desirable. This method has been found by the writer to give better results than boiling with successive portions of water. Another method is to boil for 1/2 hour with 250 _c.c._ of water, then pour the whole on a filter, wash with boiling water so long as a drop of the filtrate blackens paper moistened with a dilute solution of ferric acetate, and finally make up to 1 _litre_. Many materials, however, clog the filter to such an extent that washing is almost impossible. Kathreiner has used 15 _litres_ of water, and corresponding quantities of material, in a large steam-jacketed copper pan, for each exhaustion, making the weight up finally to 15 _kilos._, with very uniform and excellent results. (See also p. 130.) With all materials which deposit ellagic acid or other insoluble derivatives, on cooling and standing, considerably higher results will be obtained if the titration be made as soon as the liquor is cold, than if it be allowed to stand 24 hours; in this respect, a uniform practice should be adhered to. Addition of 1/2 _c.c._ of glacial acetic acid renders the infusions less liable to change.