1918.] The N.Z. Journal of Science and Technology. 
75 
“ Perchlorate Method. 
“ The procedure adopted was as follows : When iron, alumin um, or 
other salts are present, as in ordinary acid soil extracts, ashes, &c., the 
solution of the chlorides is evaporated to dryness in a porcelain dish and 
ignited for about a quarter of an hour at dull-red heat so as to throw out 
iron, &c., as oxides, as in Neubauer’s simplified method ( Landw . Vers . St., 
1905, vol. 63, p. 141). The ignition should be continued so long that, on dis¬ 
solving, a colourless solution, free from iron, is obtained. (When sulphates 
are present in large amount, after the liquid has evaporated to dryness 
5 to 10 c.c. of saturated barium hydroxide solution is added to precipitate 
S0 4 . The evaporation and ignition are then completed as usual.) The 
soluble alkali salts are then extracted with boiling water as completely as 
possible, breaking up the iron-oxide residue with a glass rod during the 
extraction. The aqueous extract is filtered into a glass evaporating-dish 
(3jin. diam.), care being taken to extract all the alkali salts from the 
residue ; this is usually complete with a volume of hot water sufficient to 
fill the 3jin.- dish, but if any doubt exist another 50 c.c. of boiling water 
can be used. The aqueous extract is now evaporated nearly to dryness 
after adding 2*5 c.c. of perchloric acid solution, sp. gr. 1-125* (20 per cent.) ; 
the evaporation must be carried to the point of vigorous evolution of heavy 
white fumes of perchloric acid. A sand-bath not too strongly heated is the 
most suitable means of effecting evaporation.f The soluble perchlorates 
are now taken up by stirring with 20c.c. of 95-96 per cent, alcohol, and, 
after settling, the clear solution poured off through a 9 cm. filter-paper, 
which has been dried to constant weight at 100° C. in a stoppered weighing- 
bottle (lj in. diam. by 2 in.). 10 c.c. of 95 per cent, alcohol is now added 
containing 0-2 per cent, of perchloric acid,J and the insoluble potassium 
perchlorate transferred as completely as possible by means of it to the 
weighed filter-paper. In washing the last traces of precipitate into the 
filter-paper another 20 or 30 c.c. of the alcohol containing 0-2 per cent, 
perchloric acid is used, and finally the perchloric acid itself is washed out 
of the filter as completely as possible by using a minimum of 95 per cent, 
alcohol. For this purpose the washings are tested, until quite free from 
acidity, with sensitive litmus paper. Care must be taken that the top 
edge of the filter-paper is washed well. The freedom of the filter-paper 
from perchloric acid is shown by its not blackening during the subsequent 
drying in the oven at 100°. The use of a glass dish for the evaporation of 
the solution in the early part of the process greatly simplifies the complete 
removal of the last traces of the perchlorate precipitate to the filter-paper, 
as these last traces are then plainly visible. In washing, a total quantity 
of 120-150c.c. of 95 per cent, alcohol can be safely used without causing 
any perceptible loss of potassium perchlorate, although so much is not 
usually necessary unless much NaCl is present. After washing, the filter- 
paper and precipitate are dried in a steam-oven for about twenty minutes,, 
whilst still in the funnel; the filter-paper plus precipitate is then trans¬ 
ferred to its weighing-bottle and the drying completed until the weight is 
constant. 1 mgm. KC10 4 = 0-3401 mgm. K 2 0. 
44 A Gooch crucible or Soxhlet tube can also be employed for collecting 
the potassium perchlorate, but if this is used care must be taken that the 
* This quantity is sufficient in most cases, but if the quantity of KC1 + NaCl exceeds 
0-2 grm., 5 c.c. of perchloric acid or more should be used. It is necessary only to take 
about one and a half times the quantity of HC10 4 theoretically necessary to decompose 
all the salts present. 
f If the liquid evaporates to dryness no harm is done so long as there is no loss 
by spurting. It is only necessary to take up with a drop of two of perchloric acid 
solution. 
f Made by adding 5 c.c. 20 per cent, perchloric acid to 500 c.c. 95 per cent, alcohol.. 
