Grains. Acetic acid (anhydrous) 11·59 ” ” (hydrated or glacial) 13·64 Citric acid (crystallised) 15·23 Hydrochloric acid (dry or gaseous) 8·29 ” ” (sp. gr. 1·16) 24·78 Nitric acid (anhydrous) 12·27 ” ” (sp. gr. 1·5) 15·23 ” ” (sp. gr. 1·42) 20·45 Oxalic acid (crystallised) 14·32 Sulphuric acid (anhydrous) 9·09 ” ” (sp. gr. 1·845) 11·14 Tartaric acid (anhydrous) 15·00 ” ” (crystallised) 17·05 2. A convenient modification of the preceding method of acidimetry consists in using the common apparatus figured in the margin and employing fused chloride of calcium to dry the evolved carbonic acid gas, instead of concentrated sulphuric acid. The mode of conducting the process and obtaining the results is precisely the same as in that last explained, and need not, therefore, be repeated. In this case, however, suction must be applied to the small tube (_g_), instead of (_d_) in the accompanying engraving. _Obs._ These methods, though apparently complicated, are not difficult to perform, when once well understood. The application of heat after the completion of the operation is indispensable, as, if it were neglected, from 0·3 to 0·4 of a gr. of carbonic acid would be retained in the liquid. The bicarbonate of soda must be pure, and perfectly free from any neutral carbonate or sesquicarbonate of soda. To ensure this, the bicarbonate of commerce is reduced to a uniform powder, put into a glass jar, and covered with its own weight of cold distilled or rain water, and allowed to stand for twenty-four hours, with frequent stirring. It is then placed upon a funnel, the tube of which is stopped with loose cotton, so as to allow the lye to drain off. It is next washed several times with small quantities of cold distilled or rain water, and after being dried by pressure between some sheets of blotting-paper, without the aid of heat, is kept for use in a well-closed glass bottle. Before use, it may be tested to ascertain its purity. If pure, it neither reddens turmeric paper, nor gives a brick-red precipitate with a solution of bichloride of mercury. Pure bicarbonate of potassa may be used instead of bicarbonate of soda; but in either case it is always proper to use an excess, so as to leave some undecomposed carbonate after the operation has ended. The presence of a little sodium chloride or sulphate in the bicarbonate will not interfere in the least, but the absence of every trace of neutral carbonate is a _sine quâ non_. [Illustration: