The method generally adopted for the determination of potassa in
manures, i. e., the direct incineration of the sample, may in certain
cases occasion considerable errors in consequence of the volatilization
of a portion of the potassium products.

To avoid this inconvenience, the author proposes a preliminary treatment
of the manure with sulphuric acid at 1.845 sp. gr., to convert potassium
nitrate and chloride into the fixed sulphate. The sulphuric acid attacks
the manure energetically, and much facilitates the incineration, which
may be effected at a dark red heat. The ignited portion (10 grms.) is
exhausted with boiling distilled water acidulated with hydrochloric
acid, and the filtrate, when cold, is made up to 500 c. c. Of this
solution 50 c c., representing 1 grm. of the sample, are taken, and,
after being heated until close upon ebullition, baryta-water is added
until a strong alkaline reaction is obtained. The sulphuric and
phosphoric acids, alumina, magnesia, etc, are thus precipitated. The
filtrate is heated to a boil, and mixed with ammonia and ammonium
carbonate, to precipitate the excess of baryta in solution. The last
traces of lime are eliminated by means of a few drops of ammonium
oxalate. The filtrate is evaporated down on the water-bath, and the
ammoniacal salts are expelled by carefully raising the temperature to
dull redness. After having taken up the residue in distilled water it
is treated with platinum chloride, and the potassium chloro-platinate
obtained is reduced with oxalic acid. The quantity of potassa present
in the manure can be calculated from the weight of platinum
obtained.--_Bull. de la Soc. Chim. de Paris_.

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