: ; ORGANIC ANALYSIS. 
within three-quarters of an inch of the large 
end, the chloride broken into fragments about 
the size of peas, is put, and a loose piece of 
cotton-wool, occupying another quarter of an 
inch, thrust in; the opening is then closed by 
a cork, through which passes a bit of straight 
tube, rather larger in the bore than that at- 
tached to the bulb, and projecting about an 
inch outside the whole; the cork is trimmed 
close to the large tube and covered neatly with 
f melted sealing-wax; and, lastly, air is drawn 
through the apparatus by the mouth to ascer- 
tain that no obstruction exists. It is now ready 
for use: after two or three experiments the 
chloride should be renewed, or there will be a 
danger of the gases being imperfectly dried. 
The tube when not in use must always be 
placed in a rack with the bulb end uppermost 
to prevent the loss of any small pieces of chlo- 
ride. Concentrated sulphuric acid may be 
advantageously substituted for chloride of cal- 
_ cium in the drying tube. In this case the 
_ tube is filled with fragments of pumice-stone; 
_ these are moistened with the oil of vitriol, and 
_ the apparatus is fitted up as usual, excepting 
that the employment of the cotton-wool is dis- 
pensed with. 
__ The combustion tube is then prepared by 
_ selecting a sound elastic cork, which is made 
- accurately to close the mouth of the tube; it is 
_ pierced with a round file, and fitted firmly 
ri pee the fine tube proceeding from the bulb 
_of the drying tube; the cork is then well 
dried on the sand-bath, and forms the medium 
bu ee naetion between the retort and drying 
tube. 
The potash apparatus is one invented by 
 Liebig, represented in fig. 430, e. It consists 
of a fine but stout tube, upon which is a series 
of bulbs, three in the middle horizontal part 
_ of the instrument, and one on each of the 
ascending limbs; one of the latter bulbs is 
made considerably larger than the other; the 
| apparatus is filled by adjusting a suction tube 
_to one of the openings, and exhausting by the 
heeks until a certain measured quantity of 
lution of potash has entered; when the 
iquid fills each of the three lower bulbs rather 
_ More than three-quarters of their capacity, suf- 
cient has been introduced. 
_ The solution of potash employed has a 
p- gr. of from 1.25 to 1.27, and must be 
‘renewed for every experiment; the portions 
‘that have been used may be put aside, and 
afterwards, when sufficient has been collected, 
May again be rendered caustic in the usual 
way by quicklime. 
_ The compound commonly used for supply- 
ing oxygen to the substance burned is oxide 
of copper, which readily imparts oxygen to 
} combustible matter in contact with it, but 
bears a very high temperature per se without 
decomposition. It is best procured by dis- 
| solving copper in pure nitric acid, evaporating 
| to dryness and decomposing the nitrate by 
| heating it strongly in an earthen crucible. Ig- 
ition is kept up till red fumes cease to appear ; 
if the heat be too great the oxide becomes 
agglutinated, and requires strong pounding in 
815 
an iron mortar to pulverize it; it however, in 
this dense state, is much less hygroscopic, and 
therefore better adapted for the purposes of 
analysis. The powdered oxide is sifted through 
a fine copper sieve, and secured in stoppered 
glass bottles. 
Immediately before each analytical ope- 
ration a sufficient quantity of the oxide is 
ignited, and while still hot transferred to a dry 
tube, by plunging the mouth of the tube into 
the oxide in the crucible and then shaking it 
in piecemeal. The tube with the oxide is 
immediately closed with a dry cork, and al- 
lowed to cool. Meantime the interior of the 
retort is completely dried by heating each por- 
tion of it in succession in the flame of a spirit- 
lamp, beginning at the closed end, and draw- 
ing air through the heated tube, by means of 
a narrower tube passed down just beyond the 
heated part and exhausting by the mouth; 
when every part has thus been dried, the 
retort is corked and allowed to cool. Five 
or six grains of the powdered and dried sub- 
stance are put into a perfectly dry test tube, 
and the whole is very accurately weighed ; its 
contents are then added to the oxide of copper 
in the mortar and the empty tube again 
weighed ; the difference gives the weight of the 
substance employed. 
The best kind of mortar is one of Wedge- 
wood ware or Berlin porcelain, capable of con- 
taining about half a pint, with a pestle com- ° 
posed of a single piece of the same material ; 
it should be thoroughly dried and well warmed. 
Much caution is requisite in charging the re- 
tort. The warm dry mortar is placed on a sheet 
of glazed paper and first cleared out with a 
little of the dried oxide of copper, which is 
put aside. Oxide to the depth of an inch is 
poured into the combustion tube; a small 
quantity of oxide is put into the mortar, then 
the substance to be analysed, then more oxide ; 
the mixture must be made quickly and care- 
fully, adding so much oxide as shall be suf- 
ficient to fill a little more than half the retort ; 
the mortar is then taken in the palm of the left 
hand and the mixture introduced, carefully 
picking it up piecemeal by the retort tube it- 
self; fresh portions of oxide are rubbed in the 
mortar to clear out the last traces, and the 
retort is then filled up with pure oxide of cop- 
per to within two inches of the extremity. 
The proportions of the mixture are repre- 
sented in fig. 430: the portion from the tail of 
the tube to the letter a consists of pure oxide 
of copper, from a to b of the mixture, from 
b to ¢ of the rinsings of the mortar, and from 
c to within an inch of the cork is again pure 
oxide. 
If the process of mixing has occupied much 
time, it may be advisable to subject the tube 
and its contents to a further operation to re- 
move any traces of moisture that may have 
been absorbed. The tube is struck smartly in 
a horizontal position on the table, to clear the 
tail-like prolongation, and to make an air-way 
above the oxide from end to end; an exhaust- 
ing syringe made fast to the table by a screw- 
vice or other convenient means, is attached toa 
