*'»
,it r
SO/LS .247
Perchlorate Method.--Potassium perchlorate is nearly insolu- Jj J
ble in 97-per cent alcohol while sodium perchlorate is quite fj! 1 1
soluble. Potassium may be precipitated and separated from jj f *
sodium by making use of this difference in solubility. A 60- (ft
per cent solution of perchloric acid is generally used. This ' j/f
solution does not deteriorate on standing and it is not dangerous 1f
to handle, as is the pure acid. It is necessary to have the solu- I
tion free from ammonium salts since ammonium perchlorate is » ^ .
only slightly soluble in alcohol. i*1;
Determination of Potassium: Perchlorate Method.1—The solution of jj ' j
potassium and sodium salts, obtained by the Smith method (page 244) is ||^ ^
used for this determination. Evaporate to about 25 cc and add 1 to 2 cc ;| '\ '
of 60-per cent perchloric acid solution. Evaporate in a hood until white M
fumes of perchloric acid appear, cool and dissolve the residue in a small |J I
amount of hot water. Again add 1 cc of perchloric acid solution and evaporate
until the solution evolves dense white fumes of'perchloric acid. Cool to
room temperature and add 25 cc of a solution made by mixing 1 cc of 60-
per cent perchloric acid with 300 cc of 97 to 98-per cent alcohol. If the jj
insoluble potassium perchlorate is caked it should be broken with a stirring \t f
rod so that no soluble salts will escape the action of the alcohol. j<|
During the process of evaporation of the various solutions a Gooch filter [i '•
should be prepared, the asbestos felt being washed with the perchloric acid- |M ;
alcohol mixture. The filter is dried for one hour at 120° to 130°, cooled and if t f
weighed. Filter the solution on this prepared filter, removing every trace }{ ^ i
of the precipitate from the beaker by means of a policeman and the prepared |11
washing solution, and wash four or five times with this solution. Dry for *j j'
one hour at 120° to 130°, cool and weigh. I \ \
From the weight of potassium perchlorate thus obtained calculate the I \ J
per cent of potassium in the sample. | |
Loss on Ignition.—Loss due to igniting the soil in contact with
air includes that due to the volatilization of ammonium salts
and water of hydration, to combustion of organic matter, and to
decomposition of carbonates and sulphides. This loss may be if 4^
reduced, in some instances, by the oxidation of ferrous iron. « ^ '<
Determination of Loss on Ignition.—The samples of dry soil obtained in
the moisture determination are heated slowly to redness in a muffle furnace,
using the same crucibles, until the organic matter is destroyed. The
crucibles are then cooled in a desiccator and weighed and the per cent
of loss is calculated.
1ScHOLL, /. Am. Chem. Soc., 36, 2085 (1914). Bit
111