WATER, SEA 



1101 



2099 



r 



never oxidised. Though not plentiful as a natural body, Mr. Spencer had succeeded 

 in forming it artificially, from several iron ores, at a very reasonable rate. Though 

 the magnetic oxide he had obtained from the white carbonate of iron was very effective, 

 yet it had a tendency to be reduced to fine powder by attrition. He became apprehen- 

 sive, therefore, that this circumstance might ultimately interfere with the rapidity of 

 his filtering operations. This led him to seek some mode of procuring an equally 

 effective though less friable body. After various experiments, he succeeded be- 

 yond his anticipations. By very simple means, he had obtained a magnetic body 

 combined with carbon from the hitherto refractory Cumberland haematite. This new 

 compound body, which is thus added to metallurgical chemistry, consists of iron, 

 oxygen, and carbon an equivalent of each ; its atomic number is therefore 42. It 

 is very hard, and when polished, has a black metallic lustre. It is highly magnetic, 

 and was said to be as incorrodible as gold or platinum. Its purifying powers were 

 stated to be very great. It can be manufactured cheaply. Mr. Spencer named 

 it protocarbide of iron. He stated that it was not always necessary in practice to 

 have an equivalent of carbon combined with the oxide, as a smaller proportion con- 

 ferred the requisite hardness, in which case it was prepared more quickly ; but, in 

 making, if kept at a low red heat along with uncombined carbon for a longer time, 

 the combination took place in equivalent proportions. 



WATER, SEA rendered fresh. The analyses of sea water which have been 

 made at various times, and the results of which will be found elsewhere, prove that 

 that liquid contains from 3| to 4 per cent, of saline substances, 

 two-thirds at least of which are common salt, and also a certain 

 quantity of organic matters, all of which substances impart to 

 it its well-known taste and odour, and render it unfit for drink- 

 ing or other domestic purposes. 



To render sea water drinkable, and thus avoid the accidents 

 resulting from an insufficient supply, or from an absolute want 

 of fresh water, in sea-voyages, is a problem which may be said 

 to have engaged the attention of men from the very moment 

 they ventured to lose sight of the friendly shore and became 

 navigators ; gradually, as the enlargement of commercial opera- 

 tions extended the length of sea-voyages, the difficulty of pre- 

 serving in a pure state the fresh water taken in store, the 

 necessity of putting up at stations for procuring a fresh supply 

 of it when it is exhausted, the great gain to be realised by 

 being enabled to devote to the stowage of cargo the valuable 

 space occupied by water-tanks and water-casks, have induced 

 many people at various times, and for many years past, to 

 contrive apparatus by means of which sea water would be 

 rendered fit to drink, or by means of which good fresh water 

 could be obtained therefrom. 



Fresh water can bo obtained from sea water in two ways : 

 the one by distillation, the other by passing it through a layer 

 or column of sand, or of earth, of sufficient thickness or length. 

 In effect, if sea water be poured at A ( fig. 2099), into a pipe 1 5 feet 

 high, and full of clean dry sand, the water, which will at first 

 flow at B, will be found pretty fresh and drinkable, but as the 

 operation is continued, the water which flows at B soon becomes brackish ; the 

 brackishness gradually aiigmenting, until, in a very short time, the water which 

 flows at B is actually more salted than that poured at A ; because the latter dissolves 

 the salt which had been first retained by the sand, which must then be renewed, or 

 washed with fresh water, a process evidently useless for the purpose in question. 

 This phenomenon, according to Berzelius, is due to the interstices between the grains 

 of sand acting as capillary tubes; and as, at the beginning of the operation, the effect 

 depends more on the attraction than on the pressure of the liquid poured in one of the 

 branches of the tube, the salt is partly separated from the water which held it in 

 solution, the latter lodging itself into the interstices of the sand, and filling them ; if, 

 when the mass of the sand is completely wetted, a greater quantity of sea water is 

 poured upon it, the weight of the said sea water first displaces and expels the fresh 

 water ; but as soon as the interstices of the sand have thus been forcibly filled up with 

 sea water, the water flowing at B becomes more and more salted ; wherefore this filtra- 

 tion cannot yield more fresh water than can be contained in the interstices of a column 

 of sand of a certain length, and proportionate to the saltness of the sea water. 



Howbeit, the removal of the salt from sea water, so as to obtain fresh water there- 

 from, is, practically speaking, an impossibility, except by evaporation. 



At first sight one would think that it is sufficient to submit sea water to distilla- 



