CHEMISTRY. 
may be cut without difficulty by a faw wliofe teeth are 
fet wide, and very eaiily admit of being fcraped, drilled, 
or ground with fand, to give them the requifite figure. 
In Dr. Lewis's conftrudlion, the crucibles which are in¬ 
tended to be applied to each other, are ground flat upon 
a Hone, with a little fand, the holes are fawed with the 
common compafs-faw of the carpenters, and are made 
a little narrower externally than internally, by which 
means it is eafy to fit them with Hoppers. Three or four 
hoops of copper-wire, about the thicknefs of a crow-quill, 
and firft foftened by heating it red hot, are faftened round 
the pots in the moll convenient places, to render them 
more durable by keeping their parts together, after they 
may have been cracked. A thin copper hoop ferves to 
fiecure the place of junction o f two pots. Large crucibles, 
from twelve to fifteen inches high, are alfo employed for 
portable furnaces ; and are capable of a vaft number of 
operations. The conftru&ion of one of thefe is given in 
the above-mentioned plate, viz. Fig. 5, Ihews the cruci¬ 
ble, perforated on its lower part, and fupported by a 
Hand. The cover is made of iron-plate, or tile. Its 
fmaller circular holes ferves to put in additional fuel, and 
to give vent to the air. It may alfo be provided with a 
moveable chimney. The larger hole admits the land-pot, 
with the retort, or other veflel. Fig. 6 , is a fefition of 
the furnace and grate. Fig. 7, the fand-pot, which alfo 
may ferve for a water-bath, or for calcining. 
Every effect of the moll violent heat of furnaces may 
be produced by the flame of a candle or lamp, urged up¬ 
on a fmall particle of any lubllance, by the blow-pipe. 
This inllrument confilts merely of a brafs-pipe about one- 
eighth of an inch diameter at one end, and the other ta¬ 
pering to a much lefs fize, with a very fmall perforation 
for the wind to efcape. The fmaller end is bent on one 
fide. For philofophical or other nice purpofes, the blow¬ 
pipe is provided with a bowl or enlargement towards the 
fmall end, in which the vapours of the breath are con- 
denfed and detained, and alfo with three or four fmall 
nozles, with different apertures, to be flipped on the 
fmaller extremity. Thefe are of ufe when larger or fmaller 
flames are to be occafionally ufed, becaufe a larger flame 
requires a large aperture, in order that the air may effec¬ 
tually urge it upon the matter under examination. See 
this inllrument at fig. 8, in the plate. 
There is an artifice in the blowing through this pipe, 
which is more difficult to defcribe than to acquire. The 
effedl intended to be produced is a continual ftream of 
air for many minutes, if neceflary, without ceafing. This 
is done by applying the tongue to the roof of the mouth, 
fo as to interrupt the communication between the mouth 
and the paffage of the noftrils; by which means the ope¬ 
rator is at liberty to breathe through the noftrils, at the 
fame time that by the mufcles of the lips he forces a con¬ 
tinual ftream of air from the anterior part of the mouth 
through the blow-pipe. When the mouth begins to be 
empty, it is replenifhed by the lungs in an inftant, while 
the tongue is withdrawn from the roof of the mouth, 
and replaced again in the fame manner as in pronounc¬ 
ing the monofyllable tut. In this way the ftream may 
be continued for a long time without any fatigue, if the 
flame be not urged too impetuoufly, and even in this 
cafe no other fatigue is felt than that of the mufcles of 
the lips. 
A wax candle of a moderate fize, but thicker wick 
Shan they are ufually made with, is the moft convenient 
for occafional experiments; though a tallow candle will 
do. The candle fiiould be fnuffed rather fhort, and the 
wick turned on one fide towards the objeil, fo that a part 
of it fhould lie horizontally. The ftream of air mult be 
blown along this horizontal part, as near as may be with¬ 
out linking the wick. If the flame be ragged and irre¬ 
gular, it is a proof that the hole is not round or fmooth ; 
and if the flame have a cavity through it, the aperture 
of the pipe is too large. When the whole is of a, proper 
figure and duly proportioned, the flame confilts of a neat 
Vox, IV. No, 189. 
193 
luminous blue cone, furrounded by another flame of a 
more faint and indiftindt appearance. The ftrongeft heat 
is at the point of the inner name. The body intended to 
be adted on, by the biow-pipe ought not to exceed the 
fize of a pepper-corn. It may be laid upon a piece of 
clofe-grained well-burned charcoal, unlefs it be of fuel* 
a nature as to fink into the pores of t hat lubllance, or to 
have its properties affedted by its inflammable quality. 
Such bodies may be placed in a fmall fpoon made of pure 
gold or fiiver, or platina. Many advantages may be de¬ 
rived from the ufe of this Ample and valuable inltru- 
ment. Its fmallnefs, which renders it fuitable to the 
pocket, is no inconfiderable recommendation. The moft 
expenfive materials, and the minuteft fpecimens of bo¬ 
dies, may be ufed in thefe experiments, and the whole 
procefs, inftead of being carried on in an opake veil'd, 
is under the eye of the obferver from beginning to end. 
It is true, that very little can be determined in this way 
concerning the quantities of produdls ; but, in moft cafes, 
a knowledge of the contents of any lubllance is a great 
acquifition, which is thus obtained in a very Ihort time, 
and will at all events ferve to Ihew the bell and lealt ex¬ 
penfive way of condudling proceffes with the fame mat¬ 
ters in the larger way. 
The blow-pipe has defervedly, of late years, been con- 
fidered as an elfential inllrument in a chemical labora¬ 
tory, and feveral attempts have been made to facilitate 
its ufe by the addition of bellows, or feme other equiva¬ 
lent inftruments. Thefe are doubtlefs very convenient, 
though they render it lefs portable for mineralogical re- 
Tearches. It will not here be neceflary to enter into any 
delcription of a pair of double bellows fixed under a 
table, and communicating with a blow-pipe which palfes 
through the table. Smaller bellows, of a portable fize 
for the pocket, have been made for the fame purpofe. 
The ingenious chemift will find no great difficulty in. 
adapting a bladder to the blow-pipe, which, under the 
preffure of a board, may produce a conftant ftream of 
air, and may be replenilhed, as it becomes empty, by 
blowing into it with bellows, or the mouth, at another 
aperture furnifhed with a valve opening inwards. The 
chief advantage thefe contrivances have over the com¬ 
mon blow-pipe is, that they may be filled with vital or 
dephlogifticated air, which increafes the a£li vity of com- 
buftion to an aftonilhing degree. Little need be faid 
concerning the manner of making experiments with fluid 
bodies in the common temperature of the atmofphere. 
Bafons, cups, phials, matraffes, and other fimilar veffels, 
form the whole apparatus required for the purpofe of 
containing the matters intended to be put together; and 
no other precaution or inllru6lion is required than to ufe 
a veflel of fuch materials as (hall not be corroded or alli¬ 
ed upon by its contents, and of fufficient capacity to ad¬ 
mit of any fudden expanfion or frothing of the fluid, if 
expedited. This veflel muft be placed in a current of air, 
if noxious fumes arife, in order that thefe may be blown 
from the operation. The more complicated, and very 
elegant chemical machines, which have, within a very 
few years paft, been invented, fliall be deferibed as we 
come to fpeak of their ufes, by which means we hope t® 
make them better known and readily underftood. 
Of OXYGEN GAS. 
Different fubftances may be ufed for obtaining oxygen, 
gas: 1. Red oxyd of mercury, or precipitate per fe. 2. 
Red oxyd of mercury by nitric acid. 3. Oxyde of man - 
ganefe, either alone or fprinkled with fulpliuric acid. 
4.. Super-oxygenated muriat of pot-afh. 5. Leaves of 
plants, &c. There are feveral other fubftances from 
which oxygen gas may be obtained ; of thofe we fhall 
fpeak as we may have occafion to detail the ufes of them. 
But, before we defcribe the proceffes for extradling oxy¬ 
gen gas, it will be proper to premife fomething on the 
general methods of obtaining gales. For this purpofe 
the pneumatic chemical apparatus muft be employed; 
3D ae 
