626 
still good to drink. In the steppes of America, 
it is astonishing with what discernment the cat- 
tle choose waters for allaying their thirst, con- 
taining minute quantities of sulphate of soda or 
common salt.” 
Waters suitable for irrigation are vastly more 
variable in the kinds, combinations, and amount 
of their impregnations, than waters suitable for 
drinking; and though they have already been 
discussed in the article Inrr@arion, the follow- 
ing notes upon them, in a recent report of the 
Scottish Agricultural Association drawn up by 
Professor Johnston, may here be introduced as 
valuable :—“ Our present knowledge of the com- 
position and wants of the growing plant, forbids 
us to ascribe to its lime alone the whole of the 
chemical influence which a water may exercise 
when employed for irrigation. Plants require 
common salt, and all natural waters contain it; 
they require sulphur, and in nearly all natural 
waters it is present; they require also magnesia 
and phosphorus and iron, and animal or vegeta- 
ble matter, and nearly all waters contain these, 
though often in quantities too minute to be 
readily detected. Hach of these substances, 
therefore, when present in water, may have its 
influence in producing the results which are 
brought about by its use in irrigation. The pre- 
cise degree of merit to be ascribed to each, will 
depend upon the proportion in which it exists in 
the water and in the soil, and upon the kind of 
plant or herbage cultivated. Asa general rule, 
it may be stated that the value of water for the 
purposes of the irrigator, depends first upon the 
quantity, and second upon the quality, of the 
solid matter it contains. That which contains 
most solid matter, other things being equal, 
should be the most valuable. To this, however, 
there are exceptions, as in the case of waters 
which, like those of the sea, or of salt springs, 
contain so much saline matter as in weather of 
ordinary drought to injure and sometimes ac- 
tually destroy the herbage; or of spring waters 
which contain so much lime as to form a depo- 
sit or incrustation on the leaves of plants. It 
| will also be understood, that, generally speaking, 
_ though a water contain a larger proportion of 
solid matter, yet if this solid matter consist al- 
most entirely of one substance, it may be less 
valuable than a water which contains a smaller 
quantity of solid matter on the whole, but in 
which a number of important ingredients occur 
in proportions more nearly resembling those in 
which they are required by plants. It is in espe- 
cial reference to such points as these that a care- 
ful analysis of waters which have been success- 
fully employed for irrigation upon our soils and 
in our climate, is both practically and theoreti- 
cally important. The four following analyses 
exhibit the composition of waters which are suf- 
ficiently abundant to be used for irrigation, but 
which are not, so far as I know, any where in 
their course employed for this purpose. 
WATER. 
River River Biglaw River 
Ale. Eye. burn, Wear. 
Organic matter...........0.0000. 175 1°64 2°58 0:92 
Potash in the state of sul- 
Hdteni aun e tad }1638 080 om 150 
Soda and chlorides............. 0:44 1:94 
Gypsum (sulphate of sana 0°64 1:46 2:94 0°88 
Carbonate of lime............ 5:28 348 7:32 7-92 
Carbonate of magnesia O00} 1:00 1:24 3°64 2:04 
Chloride of magnesium....... 1:82 080 1:25 — 
Oxidelorpnoniensscresersenreees 0°56 0:48 0°60 0 56 
Sulphuric ACL Oseesuscesesen erases 1:44 0:98 1:80 0:96 
Chlovinemersersstesrereceneoees ore 0°36 0°70 1-65 1:10 
SHU Ee cus coctocdod sacerantnaomadedcd 0:24 0:08 0:32 1:20 
14:77 =: 12:10 2476 17:08 
These waters are so far fitted for irrigation. 
that they all contain nearly every thing which 
the plant requires. That from Biglaw burn, 
however, both by the quantity and quality of the 
ingredients it holds in solution, is most likely to 
administer to the growth of plants, and to supply 
the natural or acquired deficiencies of any soil 
over which it may be made to flow.” 
Some of the chief uses of water to vegetation, 
irrespective of the nourishment which it contri- 
butes in the form of the salts and the gases held 
in solution by it, are noticed in the articles Gur- 
MINATION, ABSORPTION IN Pxiants, Drew, AGri- 
CULTURAL CuEmistTRy, and Liguip Manure; and 
some of the many chemical actions of water upon 
the constituents and the temperature of the soil, 
in their connexion with vegetation, are noticed 
in the article Draining. Water not only brings 
to plants the constituents of their food which it 
gathers and absorbs during its descent through 
the atmosphere, and during its progress on the 
surface and through the strata of the earth, but 
also acts as the solvent and the vehicle of all the 
constituents of their food obtained from manure 
and from the solid ingredients of the soil; and 
it constitutes by far the bulkier portion, not only 
of the sap which ascends within them from the 
roots to the leaves, but also of the cambium which | 
descends after the processes of evaporation and 
elaboration to form all their secretions and ex- 
cretions,—and even constitutes a main portion 
of their secreted juices, and a very considerable 
portion of their cellular and vascular substance 
or of their somewhat solid matter. See the arti- 
cles Sorm, Manurz, Sap, Campium, and Organic 
Curmistry. The chemical actions of water, in 
their joint simplicity and power, are probably 
nowhere more remarkable than within the or- 
ganisms of plants; and they no doubt play both 
a conspicuous and a manifold part in the multi- 
tudes of decompositions and recombinations 
which characterise vegetable organic chemistry, 
and particularly in those which deal with gases, 
and which reduce the elements of aeriform sub- 
stances into liquid and solid secretions. Water, 
when deprived of all its air by ebullition, has the 
power of absorbing in every 100 cubic inches of 
its bulk, under the mean temperature and pres- 
sure of the atmosphere, about 100 cubic inches of 
sulphuretted hydrogen, about 100 of carbonic 
acid, about 76 or upward of nitrous oxide, about 
124 of olefiant gas, about 3°7 of oxygen, and 
