725 



WATER. 



WATER. 



726 



of limn is of a greasy nature ; it is precipitated in, and fills up, the 

 pores of the skin ; no amount of washing in hard water can thoroughly 

 remove it ; and hence the skin can only be perfectly cleansed in rain- 

 water, hi softened hard water, or, in fact, in water that does not contain 

 soap-decomposing matters. 



Of the above constituents, the carbonates of lime and magnesia are 

 the only ones not soluble in pure water : they are kept in solution by 

 free carbonic acid [CALCIUM, Carbonate o/]. The amount of hardness 

 possessed by waters varies considerably : it is readily ascertained by the 

 SOAP-TKST. The mode of softening waters is referred to under CALCIUM, 

 Carbonate and Suljihate of. The only perfect method of removing 

 fixed matter from water is, of course, distillation ; indeed, this process 

 is carried out on board some of our ships, the water being subsequently 

 aerated for drinking purposes. On land, however, other less expensive 

 processes are available. 



The organic impurities contained in solution in water are of animal 

 and vegetable origin, the former being most objectionable. The animal 

 matter contains nitrogen, and is constantly undergoing a fermentive 

 change. Water in this state is highly dangerous to health, and should 

 be carefully avoided. Unfortunately, no test, short of rigid analysis, 

 can be relied upon for detecting this animal matter. Solution of per- 

 manganate of potash is decomposed and decolourised by it, and there- 

 fore water that discharges the colour from much of that reagent should 

 be viewed with suspicion. 



One other possible contamination of water must be noticed : it is 

 lead. Fortunately for most reasons, but unfortunately for some others, 

 water that contains an appreciable quantity of salts does not, as a gene- 

 ral rule, act upon lead. Pure distilled water acts very rapidly upon it, 

 but water that is in any degree hard does not usually affect it. Lead 

 can be easily detected in water by the blackening which occurs on 

 passing sulphuretted hydrogen gas through the water. This effect is 

 not, however, produced if only a very small quantity of lead be present. 

 In that case the water, after the passage of the gas, should be set aside 

 for twenty-four hours, when the sulphuretted hydrogen will have 

 become decomposed, and the deposited sulphur will have a dark-brown 

 or black colour if lead be present. It has been suggested to tin the 

 inside of lead pipes water not acting upon tin ; but wherever water 

 - in contact with both metals, as at a joint or flaw, a voltaic 

 action is set up, and the solution of the lead is facilitated instead of 

 prevented. 



Ettimaii'in of Water. This is accomplished either by noting the loss 

 which a body suffers on being heated, or by expelling and weighing 

 the water evolved. If the constitution of the body is well known, 

 the former method is sufficient; if not, the latter process is had 

 recourse to. 



Analijsii of Normal and Abnormal Watert. Of all special chemical 

 operations this is one of the most tedious and difficult. Usually a 

 large number of acids and bases are simultaneously present, and being 

 all in solution, cannot be so readily separated as those of perhaps a less 

 complex substance containing both soluble and insoluble matters. 

 Gaseous constituents must generally be determined at the source of 

 the water. The total amount of fixed matter is ascertained by evapo- 

 rating a known bulk of the water, and weighing 'the residue after 

 drying at '212 Fahr. If organic matter be present, the residue, dried 

 at 300 Fahr., will char on being ignited ; air having access, the carbon 

 will burn off, and the difference in weight, before and after ignition, 

 will give some idea of the amount of that organic matter. The residue 

 may then be quantitatively analysed in the same manner as any other 

 mixture of solids, or separate portions of the water may be used for 

 the purpose. The arrangement of the results of a water analysis 

 depends upon the judgment of the operator. The actual amounts of 

 each ingredient, without reference to arrangement, should first be 

 given, inasmuch as the state in which they naturally exist is liable to 

 HJII from change of temperature and dilution after rain, &c. 

 Moreover, as there are at present no data by which to determine the 

 normal condition of the acids and bases, several systems of arrange- 

 ment exist ; and if the amount of each acid and base were not given, 

 the analyses of a water by two different chemists would appear to 

 (lillrr wiili-ly wln.-ii, perhaps, they closely agree. 



\VATi:U. ix ITS PHYSICAL RELATIONS. In the preceding article 



tlie chemical history of water is briefly reviewed, and such of its pro- 



.t are described as depend, primarily, on the nature and activity 



of the molecules of which it is constituted. We now proceed to treat 



of some of those properties of water which are exhibited by masses of 



it, whether in it liquid, aeriform, or solid state ; those which render 



it a subject of physics or natural philosophy ; omitting, however, of 



such pru|icrties as it possesses in common with other bodies in 



"ruling states of aggregation, respectively, and which havo 



li.-red in the articles HYDRODYNAMICS; HYUUOMETRY* 



ilKciiAxits ; PNEUMATICS, &c. 



three states of aggregation in which water, like all kinds of 



ponderable matter, as HI; have reason to bcliuvu, can exist, are all 



i'y ^ natural; though, as in the caeo of every other substance also, 



Weaninottr j'f.ion as tho un.st natural in which 



i'jiuly subject to our observation. '1 his, 



with i -iter, in the liquid, as with all metals but one it is the 



1 1 1< nine, ammonia, and other elementary as well as 



mid nul.'Stanci-.f, it is th>; a ; rii.jim state; omitting here any 



reference to those gaseous bodies which have not yet been reduced to 

 another state of aggregation. 



We begin with the physical properties of water in the solid form, 

 considering, first, those which it manifests to sensible observation. 



In the article ICE the property is described, in virtue of which 

 two portions of that substance in a moist state, when brought into 

 contact, become one. That such is the fact has of course been known 

 from time immemorial, but it had always been referred, without 

 inquiry, to the freezing effect upon water of ice at a lower tem- 

 perature [HAIL], and had never been made a subject of scientific 

 investigation until Dr. Faraday called attention to its nature and 

 philosophical importance on the 7th of June, 1850, at one of the 

 Friday evening meetings of the members of the Royal Institution of 

 Great Britain (Albernarle Street, London) ; assemblies in which, from 

 the year 1825 downwards, so many new facts and applications in science 

 and new interpretations of facts have for the first time been publicly 

 made known, or first publicly demonstrated by experiment. To thia 

 property of ice the term regelation was afterwards applied by Professor 

 Tyndall, in a paper ' On-the Structure and Motion of Glaciers,' by 

 himself and Professor Huxley, read before the Royal Society on 

 January 15, 1857 (' Proceedings,' vol. viii. p. 331), and published in 

 the ' Philosophical Transactions ' for that year. In this paper Pro- 

 fessor Tyndall describes some experiments illustrative of the practical 

 consequences of regelation, and of their manifestation on the great 

 scale in nature. The entire subject forms so important a part of the 

 history of water in its solid condition, that it is requisite to return to 

 it here. 



In the article ICE we noticed Professor Tyndall's conclusion that the 

 plasticity of ice at 32, in mass, arising from fracture and regelation, in 

 continued and indefinite succession, imparts to it a deceptive semblance 

 of viscosity, which it really does not possess. By virtue of this process, 

 in his experiments, spheres of ice were flattened into cakes, and 

 squeezed into transparent lenses. A straight prism six inches long 

 was passed through a series of moulds augmenting in curvature, and 

 finally came out bent into a semi-ring. A lump of clear ice placed in 

 a hemispherical cavity, and pressed upon by a protuberance not large 

 enough to fill the cavity,' was converted into a hard transparent cup. In 

 the experiments with the prism, four moulds, gradually augmenting in 

 curvature, were made use of in succession. In passing suddenly from the 

 shape of one to that of the other the ice was fractured, but the pres- 

 sure brought the separated surfaces again into contact, aud caused them 

 to (regelate) freeze together, thus restoring the continuity of the mass. 

 The fracture was in every case both audible aud tangible it could be 

 heard and it could be felt. A series of cracks occurred in succession 

 as the different parts of the ice-prism gave way, and towards the con- 

 clusion of the experiment the crackling in some instances melted into 

 an almost musical tone. 



These facts have been applied by Professor Tyndall to explain the 

 phenomena of the motion of glaciers. [GLACIERS, in NAT. HIST. Div.] 

 This is a most important subject: the very introduction into the 

 philosophy of glaciers of the principle of regelation, " without which," 

 Professors Tyndall and Huxley remark, " it may be doubted whether 

 the existence of a glacier would be at all possible," and the relation of 

 which to glacier action the former was the first to discover, opens in 

 itself a new field of investigation. For the details of this application 

 we must refer to the original paper ; but the following is a summary 

 view of the subject, derived partly from that and partly from a more 

 brief account given in the ' Proceedings ' of the Royal Institution, 

 vol. ii. p. 322. 



All the phenomena of motion in glaciers, on which the idea of the 

 viscosity of ice has been based, are brought by such experiments as 

 those recited above into harmony with the demonstrable properties of 

 ice. The glacier valley is a mould through which the ice is pressed 

 by its own gravity, aud to which it will accommodate itself, while pre- 

 serving its general continuity, as the " hand-specimens " (to use a term 

 familiarly applied to rocks) do to the moulds made use of in the 

 experiments. Two confluent glaciers unite to form a single trunk, by 

 the regelation of their pressed surfaces of junction. Crevasses are 

 closed up, and the broken ice of a cascade, such as that of the T alefre 

 or the Rhone, is recompacted to a solid continuous mass. " But if the 

 glacier accomplish its movement in virtue of the incessant fracture and 

 regelation of its parts, such a process will be accompanied by a crack- 

 ling noise, corresponding in intensity to the nature of the motion, 

 and which would be absent if the motion were that of a viscous body. 

 It is a well-known fact that such noises are heard, from the rudest 

 crashing and quaking up to the lowest decrepitation, and they thus 

 receive a satisfactory explanation.' It is manifest" also "that the 

 continuity of the fractured ice cannot be completely and immediately 

 restored after fracture. It is not the same surfaces that are regelated, 

 and hence the coincidence of the surfaces cannot be perfect. They 



The founds sometimes heard during the appearance of the Polar Lights, 

 d supposed to be produced by them [TKUHF^IUIAL I.IOHT], have been referred 

 >y llumboldt to the mechanical changes continually going on in the ice-fields 

 ind p;icks of the regions in which those lights, in their most extensive and 

 irilluint development, have been principally observed. Many of these changes 

 Hunt be identical with those of glaciers ; and in the facts and rr-a-nmii.-c 

 uilduced by Professor Tynd.il!, as above, we probably have the final explanation 

 of tliis disputed subject. 



