678 CANTHARIDIN. 
for glanders and for extreme debility. See the 
articles Buistpr and GLANDERS. 
| CANTHARIDIN. The vesicating principle of 
the cantharides, or Spanish fly ; it is white, in 
small crystalline scales, insoluble in water and 
cold alcohol, soluble in ether, boiling oils and al- 
cohol, from which it precipitates by cooling. The 
| vesicating properties could be extracted from 
cantharides by oil of turpentine, and probably a 
_ satisfactory ointment be prepared by merely eva- 
porating the oil of turpentine at a moderate tem- 
| perature. 
CANVAS SHEDS. Tarpaulin sheds for afford- 
ing shelter to sheep. They are particularly valu- 
able in bleak highland districts where timber is 
| scarce and high-priced; and can be maintained 
in even woodland districts, at a less cost than 
timber sheds. Each may be formed of light and 
closely- woven tarred canvas; it may be made 
about two yards wide, and about forty yards long, 
or of any length to correspond with the princi- 
pal folds; it may be erected along a stone-wall 
of about 53 feet high, so as to have the wall for 
its back, and may easily be made water-tight 
along its line of junction with the edge or sum- 
mit of the wall; it may be erected and made 
firm with common posts and head - rails, one 
range of posts being placed along the back, an- 
other range placed along the front, and the lat- 
ter only three feet high, and multitudinously 
connected with the former by transverse head- 
rails or very slender rafters; it may be tied at 
so very many points to both the longitudinal and 
the transverse head-rails as to offer perfect re- 
sistance to any force of wind which might other- 
wise raise or disturb it; and it may be provided 
along the back with simple racks, for holding 
the sheep’s food. A simple contrivance like this 
| will keep sheep exceedingly snug amid the storms 
of winter; it would be of great value during the 
sheep-shearing season, in a rainy district; and 
something similar to it might be eminently ser- 
viceable for sheltering cattle on the grass-farms 
of Skye, and of similar bleak feeding districts of 
the Hebrides or the Scottish Highlands. 
CAOUTCHOUC. A vegetable principle exist- 
ing in the milky juices of many genera and spe- 
cies of plants; and hence there may be several 
varieties of it. It is obtained from the Siphonia 
elastica, S. Cahuchu of 8. America; Artocarpus 
incisa, integrifolia of the West Indies; Urceola 
elastica of Sumatra and Java; Micus elastica, re- 
ligiosa, indica, &c., of the East Indies; farther 
from the Castilleja elastica, Cecropia peltata, Hip- 
pomene biglandulosa. It exists in the milk of 
| many Euphorbiaceze, Papaveraceze, in Lactuca, 
Asclepias, Leontedon, &c., &c. When any of 
| these plants is incised, there exudes a milky 
juice, which, by exposure to the air, gradually 
lets fall concrete caoutchouc. The juice is pale 
yellow, thick, and similar to cream ; its odour is 
_ sourish and putrid ; specific gravity = 101174; 
| | hewn spread in thin layers on a solid body it 
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soon becomes solid caoutchouc, amounting to 45 
per cent. of the weight of the juice. Faraday’s 
analysis of the juice gave, caoutchouc 31°7 ; albu- 
men 1'9; a bitter nitrogenous matter, soluble in 
water and alcohol, and precipitable by nitrate of 
lead, 7°13; a substance insoluble in water and 
alcohol 2:9; water with a little free acid 56:37. 
The caoutchouc floats in it in globules, and it is 
immediately congealed by heat or alcohol; the 
particles deposit by standing; it is miscible in 
all proportions with water. 
Caoutchouc has a pale yellow colour, and is 
destitute both of taste and smell. The black 
colour of caoutchouc is owing to the method of 
drying it after it has been spread upon moulds ; 
by exposing it to smoke, after each successive 
coat. At 32° it is hard, and has little elasticity, 
but when heated to 60° or 70°, becomes soft and 
pliable like leather, is exceeding elastic and ad- 
hesive; and cannot be broken without consider- 
able force. 
Caoutchouc is insoluble in water, alcohol, 
acids, or alkalies; by long boiling in water it 
softens and swells up, and is then acted on 
with greater facility by different menstrua, but 
when exposed to the air, it resumes its former 
state. Caoutchouc is slightly soluble in ether. 
Dilute acids do not act upon it. Sulphuric 
acid dissolves it after long digestion without 
forming tannin; when heat is applied, it is con- 
verted into a terebinthic mass. It is rapidly 
acted on by fuming nitric acid, nitric oxide being | 
evolved. Muriatic acid does not affect it. It is 
not attacked by gases, such as chlorine, sulphu- 
rous, fluosilicic, but easily by nitrous vapours. 
When heated to a temperature of about 248°, it 
melts, and on cooling, remains in a semifluid ad- 
hesive state, but when exposed to the air in thin | 
When | 
layers, it gradually acquires hardness. 
heated sufficiently in the air, it smokes, giving 
out an odour which is not disagreeable, then takes 
fire, burning with a strong yellow flame and 
much smoke. 
tible gas, but neither carbonic acid nor ammo- 
nia; if impure it evolves all these. The chief 
product is caoutchucin or caoutchouc oil. 
Caoutchouc manufacture—This department of 
industry, which had its birth but a few years 
since, has grown so rapidly and exhibited such a 
variety of novel, ingenious, and useful applica- 
tions, within a short period of time, that it may 
already take high stand among the ancient me- 
chanical arts, since in a vast number of instances | 
it supersedes the use of woven textures, leather, 
&e. 
surface, to chemical reagents, its closeness of 
texture, &c., are qualities which will insure its 
eminence, as soon as improved mechanism shall 
enable the manufacturer to throw it into any 
required form. Wecan now observe it replacing 
woven goods to a limited extent; we find it now 
made into almost every aes vertety of tian 
When pure caoutchouc is distil- | 
led, there passes off a large quantity of combus- | 
Its elasticity, resistance to wear and tear of | 
CAOUTCHOUC. q 
| 
