622 
one thousand.” Steam, of late years, has been 
employed not only in the principal mechanical 
arts, but in the wonderful appliances of steam 
navigation aad railway travelling; in many kinds 
of manufacture, its substitution for boiling water 
has produced a perfection of process quite unat- 
tainable without its aid; and even in the culi- 
nary department, it has been employed during 
more than half a century with very great ad- 
vantage in schools and public institutions, where 
it obviates a considerable expenditure of fuel 
which would arise from water-cooking. A range 
of tin vessels, each containing its separate arti- 
cles to be cooked, are made to communicate 
with each other, and the last with a boiler con- 
taining water; and as soon as the water commences 
ebullition, the steam enters the first vessel, then 
the second, and so on to the last, which has just 
as good a share of heat as the first. Proper pre- 
cautions are taken for the escape of the steam, 
which, if confined, might cause an explosion. In 
preparing food upon an extensive scale for cattle, 
and hogs, and for the dog-kennel, steam is most 
valuable, being a much more perfect as well as 
a more economical agent. See the articles Srram 
and Sreamine-Apparatus. —In heating apart- 
ments, especially in large manufactories, steam 
is superior to every other agent, as regards both 
economy and the production of an equable and 
permanent temperature, attended by comfort, 
cleanliness, and safety. We are told by Dr. Ure, 
that a single cubic foot of boiler will heat 2,000 
cubic feet of space in a cotton-mill, having an 
average temperature of from 70 to 80 degrees. 
Again, one square foot surface of steam-pipe is 
sufficient to warm 200 cubic feet of space. Thus, 
a pipe containing little more than 27 square feet 
of surface would warm a drawing-room 24 feet 
by 20, and 12 feet high. But as the heat from 
the pipe is communicated principally by radi- 
ation, the surface of the latter should be kept 
black.—Drying operations in calico manufactories 
have for many years been effected by steam ; and 
the same agent is employed in the drying of 
gunpowder. In the rooms where steam-drying 
takes place, the workpeople remain particularly 
healthy, which is far from being the case where 
stoves are used for the drying process. The 
heating of baths by steam is also very advan- 
tageous, especially in public establishments. One 
gallon of steam will heat 18 gallons of water to 
100 degrees,—the steam being driven into the 
water through a pipe; and this heating is almost 
instantaneous. In private families, a steam-pipe, 
with a stop-cock, might communicate from the 
boiler of the kitchen-range to the bathing room. 
Besides the vapour thus generated by the tem- 
perature of boiling water, there is another kind 
of vapour of water in constant progress of vapori- 
sation, which, however, is slow and imperceptible, 
but upon which depends the very life of the or- 
ganic world. This is called evaporation. It 
takes place at all temperatures, from the burning 
WATER. 
heat of the torrid zone to the temperature of a 
Siberian winter. The atmosphere has an insa- 
tiable thirst for moisture; and takes it from all 
sources. Hvaporation into it is therefore always 
going on from the surface of the ocean, from 
that of lakes and rivers, from that of every body 
of water, however minute, and from the surface 
of the earth, from the surface of plants, and even 
from the bodies of living animals. Though more 
powerful in a warm temperature, it is still in 
activity, greater or less, at all seasons and in all 
climates; and if condensed vapour be seen rising 
from the surface of a pond during the evening in 
autumn, the same kind of vapour, though in less 
quantity, will arise when the weather is very 
cold—nay, even should the surface of the pond 
be frozen. Within the tropics, the amount of 
evaporation is enormous; and even the waters 
of the Mediterranean are supposed, every hot 
summer’s day, to diminish by evaporation to the 
amount of five hundred millions of tons; and 
they make good this loss partly by the tribute of 
rivers, and partly by influx from the Atlantic. 
The leaves, stems, and fruits of plants—nay, their 
very seeds—the respiration, perspiration, and 
excretion of animal life, all supply water to the 
air; and so does even the humus or vegetable 
soil of the earth. This universal evaporation 
accounts for the drying of anything that is wet; 
and it dries sooner before a fire than at ordinary 
temperatures, because the higher the tempera- 
ture, the more rapid the evaporation. If no 
evaporation took place, we should be unable to 
dry anything; our clothes, our houses, our arti- 
cles of manufacture or raw materials, once wet- 
ted, would ever remain so till the end of time. 
Evaporation at equal temperatures is much more 
rapid during wind than when the air is calm,— 
a fact exemplified by every washerwoman, who 
will certify that a strong breeze greatly hastens 
the drying of her clothes. If the evaporation 
from the ocean be prodigious, that from the sur- 
face of the land is not less so. Bishop Watson, 
in his Chemical Essays, states that, during a 
summer’s day in Great Britain, the evaporation 
from an acre of mown meadow-land, after the 
removal of the hay, amounts to 1,600 gallons,— 
a conclusion to which he came as the result of a 
series of experiments carefully conducted by him- 
self—But what is the use of this enormous eva- 
poration, of this unquenchable thirst of the air 
surrounding our globe? It is another beautiful 
provision of the Almighty Creator for the wants 
of organic nature; it is the life-spring of the 
animated creation. We have explained the ab- 
sorption of specific heat by steam as it is gene- 
rated from boiling water. A similar absorption 
of specific heat takes place during evaporation, 
otherwise there would be no evaporation at all, 
and the water at present evaporated would retain 
its liquid condition. This absorption of specific 
heat, being made at the expense of the surround- 
ing media, causes a sensible diminution of tem- 
