CHEMISTRY OF HORTICULTURE — WATER. 
261 
solution. The solution so obtained is termed lime-water, and this, when fresh made, and 
secured from any contact with air, is perfectly clear and colourless. 
2. To dissolve one pound of pure chalk in Water, and thus to imitate that hardness 
which exists in the Water of streams and wells, the pound of chalk must not only retain 
the seven ounces of carbonic acid that it contains as a simple carbonate of lime, but it must 
combine with a second equivalent of carbonic acid, that is, with seven additional ounces, to 
bring it to the condition of a double, or &i-carbonate of lime. “ In such a condition,” says 
Dr. Clark, “ chalk exists in the Waters of London, dissolved, invisible, and colourless, like 
salt in Water. A pound of chalk, dissolved in 560 gallons of water by seven ounces of 
carbonic acid, would form a solution not sensibly different, in ordinary use, from the filtered 
water of the Thames, in the average state of that river.” Again : — 
“ Any lime-water may be mixed with another, and any solution of bicarbonate of lime 
with another, without disturbing the clearness of either. Not so if the most pellucid lime- 
water be mixed with a clear spring or river Water, rendered hard by chalk existing in it, 
as a bicarbonate of lime. At first a haziness appears, which deepens into a milkiness, 
carried on till the mixture resembles a thin whitewash. The white particles of chalk 
gradually subside, leaving the Water above perfectly clear.” 
The chemical tyro should investigate the facts stated, and compare them with practical 
results. Dr. Clark thus applies his theory : — “ If we suppose that one pound of chalk after 
being burned to nine ounces of quick lime, be dissolved so as to form forty gallons of lime- 
water : that another pound is dissolved by seven ounces of extra-carbonic acid, so as to 
form 560 gallons of a solution of bicarbonate of lime, and that the two solutions are mixed, 
making together 600 gallons ; then the nine ounces of quick lime already in solution in 
the forty gallons will unite with the seven extra ounces of carbonic acid that hold the pound 
of chalk, dissolved in the 560 gallons of Water. Those nine ounces of caustic lime, and 
seven ounces of carbonic acid attract each other, unite to form sixteen ounces of chalk 
(simple carbonate of lime), which being insoluble in Water, becomes visible immediately on 
its being formed ; at the same time that the other pound of chalk (of the 560 gallons) being 
deprived of the extra seven ounces of carbonic acid that kept it in solution, re-appears. 
Both pounds of chalk will be found at the bottom after subsidence. The 600 gallons of 
Water will remain above, clear and colourless, without holding in solution any sensible 
quantity either of quick-lime or of bicarbonate of lime.” So far, almost verbatim, the theory 
of Dr. Clark’s patented process, which any one may bring to the test who can obtain pure 
Water and quick-lime. Minute accuracy cannot be expected from ordinary lime and 
impregnated Waters, but the essential facts can be verified. I once knew two large gardens, 
one, that of a gardener in Buckinghamshire, where, for want of a rill or other source of 
soft water, the plants were supplied from a well. On such occasion, the hard Water was 
exposed in tubs for hours ; thus a portion of carbonic acid was liberated, and a corresponding 
quantity of chalk deposited. A few grains of pure, fresh, quick-lime stirred into a gallon of 
such Water would soften it without adding a particle of lime to the fluid. So far as horti- 
culture is concerned, it is to be regretted that the process is patented, and therefore cannot 
be safely adopted in the great way ; but ere long we hope that all towns will be supplied 
with purified water. 
But hardness may not entirely depend upon chalk. I have detected gypsum (sulphate 
of lime) in water, to an extent sufficient to render it destructive of the lead bottoms of 
cisterns. The test for this substance is any one of the neutral salts of baryta, dropped into 
the clear water after it has deposited the carbonate of lime. After what has been said in 
the course of this article, we presume that no one will doubt the great utility of analytic 
chemistry to horticulture, and it is to be hoped that our rising young men will turn their 
serious attention to the science. 
