B O I 
B O I 
to support the weight of the body ; in which 
seuse it differs only from marshes or fens, as a 
f part from the whole : some even restrain the 
term bog to quagmires pent up between two 
; hills ; whereas fens lie in champaign and low 
countries, where the descent is very small. To 
dram boggy lands, a good method is, to make 
| trenches of a sufficient depth to carry off the 
I moisture; and if these are partly filled up with 
| rough stones and then covered with thorn 
[ bushes and straw to keep the earth from fillino- 
up their interstices, a stratum of good earth 
| aiul tail may be laid overall; the cavities 
! ;mi0a o the stone.s will give passage to the 
water and the turf will grow at top as if no- 
thing had been done. 
BOILING, or ebullition, in physics, the 
] agitation of a fluid body, arising from the an- 
; plication of fire, &c. 
ft has been proved that all fluid! ty is the effect 
I o. a certain quantity of caloric, or the matter 
| of heat, absorbed by a body in passing from 
| ? sohd to a fluid state, as is shewn in the melt- 
lng of ice, tallow, wax, &c. Boiling is the act 
| of a body passing from a fluid state to that of 
vapour, occasioned by a further absorption of 
1 caloric. 
If the heat is applied to the bottom of 
t he vessel containing the liquids, as is usually 
i t ie case, after the whole liquid has acquired 
a certain temperature, those particles of it 
, which are next the bottom, become elastic, 
1 2 nd rise up, as they are formed, through the 
liquid, like air-bubbles, and throw the whole 
j into a violent agitation. Tne liquid is then 
1 said to boil. 
' A pleasing experiment is related by that 
| elegant and ingenious philosopher, the pre- 
] bishop of Landaff, which is illustrative 
of the nature of boiling in general, and par- 
w-u • - of w,iat luls 'keen just advanced. 
I With an intent on of exhibiting a striking in- 
stance of the increase of dimensions produced 
J J fluids, he took a glass vessel not un- 
I like the thermometer in form ; the bulb 
contained above a gallon, the stem had a 
small diameter, and was about ' two feet in 
length. _ This vessel he filled with boiling 
| water to the very top of the stein, and corked it 
close with a common cork. The water and the 
cork were at first contiguous, but as the water 
I cooled it contracted, and sunk visibly in the 
I stem; and thus the first intention of the ex- 
pel iinent was answered. But here an unex- 
jpected phenomenon presented itself. The 
j water, though it was removed from the fire 
though it was growing cold, and had for some 
time entirely ceased from boiling, began to 
] boil very violently. When a hot iron was 
applied to that part of the stem, through 
| which the water in contracting itself had de- 
scended, the ebullition presently ceased ; it 
j was renewed when the iron was removed; 
and it became more than ordinarily violent,’ 
J when, by the application of a cloth dipped in 
! cold water, that part was cooled. To account 
ifor these appearances, it is only necessary to 
■recollect, that by the sinking of the water in 
tne stem, a kind of vacuum is left between its 
surface and the cork ; the water therefore 
necessarily boils with a lower degree of 
neat than it would under the pressure 
ol the atmosphere. The space between the 
jcork and the water is not however a perfect 
Jracuum : it is occupied either by the vapour 
j? ^ e water, or by a small portion of air, or 
©y both. Heat increases the elasticity both 
of air and vapour, and thus augments the 
pressure upon the surface of the water, hence 
the ebullition ceases upon the application of 
the hot iron. Cold, on the contrary, di- 
minishes the elasticity of the air, and con- 
denses vapour ; and thus the pressure upon 
the surface being lessened by the application 
of a cold cloth, the ebullition of the water be- 
came more violent. The heat of the water 
when it ceased boiling was 130 degrees, 
i An experiment of another distinguished 
philosopher affords perhaps a better Illustra- 
tion of tile whole theory which has been just 
advanced. This gentleman placed a quan- 
tity ol vitriolic ether under the receiver of 
an air-pump, which was so contrived that he 
was able to let down a thermometer ac plea- 
sure without admitting the external air. He 
no sooner began to extract the air, than the 
ether was thrown into a violent ebullition, at 
the same time its temperature, sunk surpriz- 
ingly. W hen the ether was first put in, its 
temperature was about 58 degrees, but it be- 
came so cold when boiling, that a quantity' of 
water in a vessel contiguous to it was suddenly 
frozen. The manner in which these pheno- 
mena may be explained is this : — —The weight 
of the atmosphere being removed, the heat 
wliicli the ether contained was sufficient to 
make it boil. J he elementary fi e which the 
ether lost in boiling was disposed of in forming 
a vapour more subtile than the ether itself; 
which could not, consistently with the prin- 
ciples established, be formed without the ab- 
sorption of a considerable quantity of the mat- 
ter of fire. Now as it appears that water and 
spirit of wine boil in vacuo at 122 degrees 
below their ordinary boiling point, it is na- 
tuial that ether, which boils in the open air 
at about the heat of the human blood, should 
boil in vacuo at 24 degrees below 0, a degree 
of cold sufficient to freeze any water that 
might happen to be in contact' with the ves- 
sel which contains the ether. 
Every particular liquid has a fixed point 
at which boiling commences, and this is called 
the boiling point of the liquid. Thus water 
begins to boil when heated to 212 decrees. 
After a liquid has begun to boil, it never be- 
comes hotter, however strong the fire mgy be 
to which it is exposed. A strong heat, indeed, 
makes it boil more rapidly, but does not in- 
crease its temperature. This fact was first 
observed by Dr. Hooke. The follow ang ta- 
ble shows the boiling point of a number of 
liquids : 
Bodies. 
iEther 
Ammonia 
Alcohol 
Water 
Mu riat of lime 
Nitric acid 
Sulphuric acid 
Phosphorus 
Oil of turpentine 
Sulphur 
Linseed oil 
Mercury 
Boilingpoint. 
98 
140 
176 
212 
230 
248 
590 
554 
560 
570 
€00 
660 . 
The boiling point however is found to depend 
on the degree of pressure to which the liquid 
is exposed. It the pressure is diminished, the 
liquid boils at a lower temperature; if it is 
increased, a higher temperature is necessary 
to produce ebullition. Fjom the experi- 
B O L 239 
mcnt of professor Robison, it appears that, 
in a vacuum, all liquids boil about 145 de- 
grees lower than in open air, under a pres- 
sure of .30 inches oBmercury : therefore water 
would boil in vacuo at 67 degrees, and al- 
cohol at 34 degrees, in Papin’s digester, 
the temperature of water may be raised to 
300 degrees, or even 400 degrees without 
ebullition ; but the instant that this great pres- 
sure is removed, the boiling commences with 
prodigous violence. 
BOLL, in mineralogy. This mineral oc- 
curs chiefly in the isle ol Lemnos, at Sienna 
in Italy, and in Silesia. Its colour is gene- 
rally ari obsciyg Isabella yellow, or reddish 
or whitish brown : it is sometimes, though 
rarely, met with of a greyish yellow, or fiedi 
led; its surface is often marked w.th black 
spots, and dendritic figures. It generally oc- 
cur-; massive ; its texture is earthy ; fracture 
concnoidal. Internally it exhibits a slight 
glimmering lustre, and acquires a polish by 
friction. \\ hen broken with a hammer it dies 
into irregular sharp-edged fragments. The 
dark coloured varieties are opaque, the lighter 
coloured are more or less translucid. i t has 
a greasy feel, adheres strongly to the tongue, 
gives a shining streak, is very soft, and is. ea- 
sily frangible. Specific gravity 1 .4 to 2.0. 
When put into water it absorbs a little 
with great eagerness, anti breaks down into 
small fragments with a crackling noise. 
W hen finely pulverized, and diffused through 
boiling water, it remains suspended a less 
time than any of the plastic clays, and is en- 
tirely separable by the iiltre. ‘ Before the 
blow-pipe it turns black and melts, without 
any addition, into a porous, greenish, grey 
nag. The Leinnian bole, according to Berg- 
man, contains ° 
47.0 Silica 
19-0 Alumina 
6.0 Carbonate of magnesia 
5.4 Carbonate of lime 
5.4 Oxide of iron 
17.0 Water and air 
99.8 
The only use of the bine at present is as a 
coarse red ingredient ; for which, purpose it is 
calcined and levigated, and is sold in Germany 
under the name of Berlin or English red. 
BOLETUS, in botany, spunk ; a genus 
of the order of fungi, belonging to the cryp- 
togamia class of plants. Botanists enumerate 
170 species, of which the following are the 
most remarkable. 
1. Boletus bovinus, or cow Spunk, is fre- 
quent in woods and pastures. It is generally 
of a brown colour, though sometimes it is taw- 
ny, yellowish brown, reddish brown, deep 
red purple, or greenish brown. The flesh is 
yellow, white, or reddish. The young plants 
aie eaten in Italy, and esteemed a great de- 
licacy. The Germans also account them a 
dainty, calling them gombas, and brat-bulz. 
Cows, deer, sheep, and swine, will feed upon 
this and other boleti, but are sometimes 
greatly disordered by them. In cows and 
other cattle they have been known to create 
bloody urine, nauseous milk, swellings of the 
abdomen, inflammations of the bowels, stop- 
pages, diarrhoeas, and death. In sheep they 
are said to bring on a sehirrhous liver, a 
cough, a general wasting, and dropsy. Scci~ 
r> f j, dermestes, and many other insects 
feed upon and breed in them abundantly. * 
