THE RARER ELEMENTS IN SOILS AND PLANTS. 19 
hot-water jacketed funnel. If there is not too much magnesium 
present these precautions will enable the analyst to obtain a pre- 
cipitate free from magnesium or nearly so. The presence of mag- 
nesium ammonium phosphate in the iron group canseasily be recog- 
nized by the appearance of crystals on the side of the beaker. When 
such precipitate appears it is best to complete the filtration and 
make a second precipitation. In this way the amount of magnesium 
is so reduced that it will seldom give further trouble. The washing 
is best done with hot water containing 5 per cent NH,Cl. After 
complete washing water containing NH,NO, is used to wash out 
the chloride prior to ignition. Some electrolyte must be used in the 
wash water, otherwise the phosphates of iron and aluminum will 
run through the filter. 
Correction for the magnesium which may be in the iron group was 
made in the following manner: After the titanium has been de- 
_ termined and the phosphoric acid precipitated 1 to 2 grams of citric 
acid are added to the solution and the magnesium precipitated with 
an orthophosphate and ammonia. A correct figure for aluminum 
can be certain only after this magnesium correction has been made. 
In cases where the manganese is below or only slightly above 0.01 
per cent none will be found precipitated with the iron group, nor is 
it necessary to correct the magnesium precipitate for such an insig- 
nificant amount. When the manganese is high, as in the raspberries, 
pine needles, and oak leaves, corrections are necessary. A simple 
colorimetric determination of the manganese in the magnesium pyro- 
phosphate gives data enabling the analyst to give a correct figure 
for magnesium. Correction is made for the aluminum in the follow- 
ing manner: The solution of the iron group, after the titanium has 
been determined and the phosphoric acid has been removed, is divided 
into two portions; in one the manganese is estimated colorimetrically 
and the magnesium correction is made in the other half. 
The precipitation of the magnesium and phosphoric acid in the 
separate halves of the filtrate from the iron group is done in the 
ordinary manner. 
THE ALKALIES. 
Great care must be used in ashing the plants, particularly when 
the rare, more volatile alkalies are to be determined. Potash is 
lost when present as the chloride, if the temperature of ignition be 
carried above a dull redness, barely discernable in the dark. In order 
to control this temperature of ignition, a special electric muffle was 
constructed. When the temperature, as measured by a pyrometer 
on the inside of the furnace and not touching the walls, did not exceed 
525° C., there was no loss of potash during ashing. This fact was 
established by comparing analyses of the same plant made using and 
