p 



SEA AND MINERAL WATERS. 177 



tration deprives water of living objects and impurities suspended in it. 

 Distillation, is the best mode of purifying water, but its taste is flat and 

 unpleasant, in consequence of the absence of air and carbonic acid. 

 The distillation of sea water for use at sea has been attempted of late 

 with what success we do not know. Pure water on shipboard, as 

 elsewhere, is a subject of great importance, as the impurities of water 

 are the cause of numerous diseases. 



Alum cleanses rnuddy water, 2 or 3 grains answering for a quart of 

 water, but renders the water harder ; it does not therefore render it 

 chemically purer. Alkaline carbonates contribute to soften water by 

 decomposing the earthy salts ; and the addition of lime precipitates 

 carbonic acid and sulphate of lime. 



Sea water includes that of the ocean and of inland seas having the 

 same composition. It varies in amount of solid matter in different 

 seas. That of the Medeterranean contains 410 grs. of solid matter in 

 1000 parts; that of the English channel 380, of the German ocean 

 from 200 to 345, the Baltic from 66 to 168. The average quantity of 

 saline matter is therefore assumed by Dr. Pereira at 3 per cent-, and 

 the mean density at 10.274. The composition is about 964 water, 27 

 common salt, 2 sulphate of magnesia, 3 magnesium, sulphate of lime, 

 with fractions of other salts. In moderate doses, it is useful in scrofulous 

 affections, as in grandular enlargements, mesinteric diseases, &c. Topi- 

 cal applications of it are stimulating, and it is used as an embrocation 

 in chronic diseases of the joints. Persons are less likely to take cold 

 after a salt water bath than a fresh water one. 



Mineral waters, like sea water, are not useful for domestic purposes ; 

 but, as drinks, they are much used for medicinal purposes. Those in 

 which iron predominates are chalybeate or feruginous. Some of these 

 contain a carbonate of iron, and are carbonated chalybeates. Some arc 

 impregnated with sulphuretted hydrogen, and have the odor of rotten 

 eggs ; these are sulphurous or hepatic waters. Some are brisk and 

 sparkling, with an acidulous taste ; these are carbonated or acidulous 

 waters, and others are saline. But these require no further notice 

 here. 



NUTRITIVE QUALITIES OF FOOD. 



We have shown that the amount of water in vegetables is very 

 great ; and that it differs in different plants ; the nutritive properties 

 therefore, depend much on this circumstance. Those substances which 

 possess little or no water, are called anhydrous, but these are not al- 

 ways nutritive, as shown under Lignine. Green resinous matters of 

 plants are likewise wanting in nutriment ; hence of the solid nutritive 

 portions of vegetable food, the woody and coloring parts are to be de- 

 ducted. Again, those constituents of plants which are called nitrogenized 



