17.55 cub. cent. of alkaline fluid, which were used for the
          saturation of the above acid, and of which 100 cub.
          cent. saturate an equal quantity of that acid.
——­
10.45 cub. cent. of the sulphuric necessary for the alkali
          contained in the soap, representing 0.1823 grms. of
          soda = 7.64 per cent.

A determination of the alkali as a sulphate afforded in another portion of soap 9.57 per cent. of soda, because the sulphate of soda and chloride of sodium present in the soap gave up their alkali.

The alkaline fluid applied by me was a saccharine solution of lime, which can be naturally replaced by a solution of soda, and must be if the chloride of sodium and sulphate of soda mixed with the soap shall be determined in the following way:—­

The fluid again exactly neutralized with alkali is evaporated to dryness, and the residue gently heated to redness.  As in the above manipulation, the fluid was not heated to the boiling point, the original chloride of sodium and sulphate of soda are contained in the weighed residue, besides the soda of the soap and that which has been added with the sulphuric acid, forming sulphate of soda.  A second exposure to a red heat with sulphuric acid converts the whole residue into sulphate of soda, and from the increase of weight, by a comparison of the equivalents of NaCl and NaO, SO_{3} the quantity of the former may be decided.  According to the equivalents which Kopp furnished in 1850, the increase of weight to the chloride of sodium is as 1:4.68.  The original sulphate of soda must be, lastly, found by the subtraction of the same salt formed plus the calculated chloride of sodium from the first heated residue.

In practice, it is seldom necessary to proceed with the determination of the chloride of sodium and sulphate of soda, except with stirred and cocoa-nut oil soaps; certainly less of the truth is seen if, after the above determination of the fatty acids and the effective alkali, the absent per centage of water is introduced in the calculation, than if the water is reckoned, which is never completely evolved from soap, even technically prepared at 302 deg.  Fahr., and another determination made of the fatty acids or alkali en bloc the fatty acids, or even the alkaline contents.

The method here given partakes of the usual imperfections, that the fatty acids as well as the unsaponified soap are equally estimated, and the mixed hydrate or carbonate of the alkali as well as the combined alkali.  The presence of the carbonate can be easily recognized by the foaming of the soap solution, upon the addition of the sulphuric acid.  These imperfections, however, are of little importance.