hillebranr] ALKALIES, CARBON DIOXIDE, CARBON. 101 
precipitate forms, which dissolves on vigorous stirring if enough of 
the precipitant w:i> used. After a time a crystalline precipitate Palls 
a double carbonate of magnesium and ammonium which is insoluble 
in a concentrated solution of ammonium carbonate. Allow to stand 
for six to twenty-four hours. Wash with the concentrated ammonium 
carbonate solution. It is probably no exercise of undue caution to 
redissolve and reprecipitate, to make sure of getting all alkali in the 
filtrate. 
The amyl alcohol meblwd. — Under certain circumstances, notably 
absence of lithium, the method of Gooch developed by Riggs 1 may be 
satisfactory. It is similar to that of Gooch for separating lithium 
from sodium and potassium chlorides by amyl alcohol, and involves 
the same solubility corrections for the alkali chlorides above noted 
(p. 100) in the description of Gooch's method. Riggs's summary is as 
follows: 
Evaporate the solution nearly or quite to dryness. Dissolve the residue in as little 
water as possible and add a few drops of hydrochloric acid. Then add :>0-40 cubic 
centimeters of amyl alcohol and expel the water by bringing the alcohol to boiling. 
Continue the boiling until the volume ef the solution is reduced to 10 cubic centi- 
meters, or even considerably less. In filtering, it is of great advantage to use a per- 
forated crucible and an asbestos felt and to filter under pressure. In case the total 
chlorides exceed 0.2 grams it may be advisable to decant the liquid, wash the residue, 
redissolve, and repeat the precipitation. If this be not done, the precipitate should be 
redissolved with the least possible quantity of water, a few drops of hydrychloric acid 
added, and the precipitation repeated in the original solution. The filtrate is trans- 
ferred to a weighed platinum dish and evaporated. Water is added before the alc< >h< >1 
has been expelled, and the evaporation continued. The residue is diss* >lved in wafer. 
Sulphuric acid is added in slight excess. This solution is evaporated to dryness, 
the residue ignited and weighed, and the treatment with sulphuric acid is repeated. 
The residue of insoluble chlorides may be transferred to the weighed perforated 
crucible and dried at a temperature below their melting points, or it may be dis- 
solved and the solution transferred to a weighed platinum dish, evaporated, and the 
residue dried as above and weighed. 
As with the Gooch method for lithium, the numerous test results are 
good. 
XXI. CARBON DIOXIDE, CARBON. 
For this estimation an apparatus (fig. 15) permanently set up is used, 
of which several forms have been described by different writers. The 
rockpowder is boiled with dilute hydrochloric acid in asmall Erlenmeyer 
flask, attached to an upward-inclined condenser, whence, after passing 
through a compact arrangement of drying tubes — first, one of calcium 
chloride, then one of anhydrous copper sulphate to retain hydrogen 
sulphide from decomposable sulphides and any hydrochloric acid that 
may pass over, and finally a second calcium chloride tube — the carbon 
dioxide is retained by absorption tubes tilled with soda-lime followed 
i Am. Jour. Sci., 3d series, Vol. XLIV, p. 103, 1892. 
