ON THE CHOICE OF A GARDEN SITE. 31 



always be given from the north and north-east winds, by judicious planting. 

 The site should be freely exposed to the south-east, south, south-west, and 

 west, unless it is near the west coast, when some shelter may be necessary 

 from the tierce winds of the Atlantic Ocean. But shelter on the north and 

 north-east is indispensable in our climate, unless we choose to see our crops 

 shrivelled up by the piercing winds that have just been robbed of all their 

 heat by wrapping themselves round the gigantic icebergs of the polar seas. 



83. Pure Water, liberally supplied, is essentially necessary to a healthy 

 site. If a brook, spring, or river, originates in or passes through it, so much 

 the better ; but as this charm cannot always be secm-ed, see that the water 

 is bountifully supplied, easily got at, and of the purest quality. It should be 

 tested by chemical analysis, and every means taken to prove that it is not 

 tainted with vegetable or mineral poisons. Neither vegetables nor animals 

 can long continue to enjoy health, unless this primary necessity of their very 

 existence is provided to them in a pure state. 



84. Eain-water is the purest that can be obtained without having recourse 

 to distillation : it contains carbonic acid and oxygen, absorbed from the atmo- 

 sphere. Spring-water filtered through granite and silicious rocks is tolerably 

 pure ; but springs which pass through limestone or chalk are impregnated with 

 considerable portions of these substances. Lake and river water partakes of 

 the soil which forms its bed or basin ; and marsh waters a.bound in decomposed 

 animal and vegetable matter. Pure water is tasteless and inodorous ; the pre- 

 sence of carbonic acid renders it bright, sparkling, and more or less acidulated, 

 as in the Carlsbad and Seltzer waters. When iron is h eld in solution by the car- 

 bonic acid, the water becomes chalybeate, as in the Cheltenham and Tunbridge 

 waters. The presence of sulphuretted hydrogen distinguishes the Harrogate, 

 IMoffat, and many other medicinal springs. Hot springs are produced by silica 

 held in solution by free soda, and formed in the vicinity of volcanic or other 

 igneous rocks. 



85. The saline taste in water ai'iscs from impregnation with earthy salts of 

 lime, of magTiesia, of common salt, and sometimes the bicarbonate of soda and 

 potash. Iron gives an inky taste to the water, and a yellowish tint to linen 

 washed in it. These salts are the cause of hardness, which filtration has no 

 effect in removing ; but it is softened by exposure to tJie air, and sometimes by 

 boiling. 



86. Availing himself of the chemical properties of chalk and lime. Dr. 

 Clarke, of Aberdeen, has invented a process for pm-ifying waters impregnated 

 with lime or chalk, a combination very common in the water round London. 

 AVlien burnt in the kiln, a pound of chalk loses seven ounces of its weight by 

 the withdrawal of carbonic acid, and becomes quicklime soluble in water ; 

 but it requires forty gallons to reduce it to lime-water. Another mode of 

 rendering chalk soluble in water is the very reverse of this : in place of with- 

 drawing the seven ounces of carbonic acid from the chalk by calcination, seven 

 ounces of carbonic acid are added to it, and it is then soluble in water without 

 perceptibly changing its appearance ; in fact, the Thames water, after filtra- 



