HILLEBRAND.] 
ALKALIES. 
97 
weight of ammonium chloride and eight times as much precipitated 
calcium carbonate. 
The ammonium chloride used must be purified, preferably by subli- 
mation, or made by neutralizing jane ammonia by pure hydrochloric 
acid, and the calcium carbonate is best obtained from pure calcite by 
solution and reprecipitation. However obtained, this last is rarely 
free from alkalies, which must be estimated once for all in a blank 
test in order to apply a correction. Eight grams of the carbonate 
will contain usually from 0.0012 to 0.0016 gram of alkali chlorides, 
almost entirety the sodium salt, but the amount has been brought 
down to half the above by very long washing. This correction may 
be admitted at once to be a defect of the method, but it is one easily 
applied with safety. 
The ignition may be made in a covered crucible of ordinary shape 
and of about 20 to 30 cm. 3 capacity, heated to dull redness for not more 
than two-fifths of its height. 
Fig. 14.— The J. Lawrence Smith crucible for alkali deter- 
minations. For dimensions see text. 
but the heat has to be kept 
so low in this case to avoid 
loss by volatilization that 
perfect decomposition is not 
always assured. Hence, to 
avoid waste of time in very 
fine grinding, the form of 
crucible with cap originally 
advocated by Smith is very 
much to be preferred, since 
it permits, when set at an 
angle through an opening in 
the side of a fire-clay cylin- 
der, of the application of the 
full heat of two burners, and perfect decomposition invariably results 
without the need of extraordinary care in grinding. The crucible used 
in this laboratory (fig. 14) for one-half gram of rock powder and 4 
grams calcium carbonate is 8 cm. long, 1.8 cm. wide at the mouth, and 
1.5 at the bottom. For double the amounts or more the dimensions 
are 8 cm., 2.5 cm., and 2.2 cm. The weights are 25 and 40 grains. 
Treatment oftlie mineral powder. — Perfectly satisfactory results are 
to be obtained with but a half gram of rock powder. This is weighed 
out, ground down somewhat finer in a large agate mortar, mixed with 
its own weight of sublimed ammonium chloride, and the two thoroughly 
ground together. Then nearly all of 4 grams of calcium carbonate is 
added and the grinding continued till a thorough mixing has resulted. 
The contents of the mortar are transferred to the long crucible, the rest 
of the carbonate being used for rinsing off mortal' and pestle. The 
crucible is then capped and placed in a day cylinder (fig. 14), or through 
Bull. 176 7 
