Page:Science vol. 5.djvu/113

 JA*lfA«T"30, IMS.)

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��{tarts, and that lictwccii surriico ami liottom waters O.Dlo2 parts, referred to a Imndred parts oT halogeD. The fact that deeper waters do oorttain more lime than surface-waters, Profes- sor Dittmar attributes to the action of life near the surface in removiDg lime from solution, and to the tendency of bottom- waters to take it up from the oceau-floor.

As is natural, the alkalinity, too, increases with depth ; and the difference between surface and bottom waters in this respect corresponded in I'rofessur Dittmar's dete mil nation to O.OU of lime, which is so near to the figui-es found in tJie direct determination of the lime, that the closeness of agi'eement must be accidental.

Concerning carbonic acid in sea-water, the evidence goes to show, that, as a rule, it is present iu insutficient amount to convert to bicarbonate that base which is in excess of the sulphuric add and halogen, and is ^e only exceptionally ; that in surface-waters it varies inversely with the temperatnre, and for equal ranges of temperature seems more abundant iu the waters of the Atlantic than in those of the Pacific Ocean. The quantities of oxygen and nitrogen absorbed by sea-water are func- tions of the temperature. Nitrogen varies within the same limits in deep aud shallow waters ; oxygen is generally present to a smaller extent than the hypothesis of surface absorption of atmospheric air. nl the lem[>er- atnre corresponding to the amount of nitro- gen found, would demand ; and the absolute amount of oxygen in waters of great depths, and occasionally in waters of only moderate depths, is ofu>n exceedingly small.

Professor Dittmar diacusaes his anal3-Ges with great elaboration, and devotes much space to chapters upon the salinity and specific gravity, bromine, carbonic acid, alkalinity and ab- sorbed gases of ocean-water. In the analysis Ihe desirability of preciseness was constantly in view. Thus, for example, much stress is laid on the necessity of toeighivg jrartions for analysis, as is usual with concentrated mineral waters: and, in the estimation of total halo- gen by Volhard's method. Professor Dittmar secures greater accuracy by weighing the pre- npitating solution of silver nitrate, and then etfecling Ihc final titrations with centesimal so- lutions of ammonium sutphocyanatc and silver nitrate. It is quite plain, however, and much to lie regretted, that the lack of water at Pro- fessor IJittmar's disposal (never exceeding, and often falling short of, two litres) has af- fected the value of the work. Very few pro- cesses of analysis can bear the mugnifving of inherent error a huiidrcilfold ; and Iflem'of sea-

��water, to which Professor Dittmar felt restrict- ed for single determinations of total halogen, is an exceedingly small |>ortion when the result is to bp c.xpresseil in grams to the litre of water. or in parts to the hiindred grains of total salts. With an adequate quantity of material at hand, 40 cni* need not hai'e been made to serve for a determination of lime and mag- nesia ; nor would such pi-ocesses as the es- timation of magnesia .is pyrophosphate, and sulphuric .tcid as barium xulphate, have been denied ordinary care lo insure the puritj' of the substance weighed. In the case of the lime, it was found, when some of the residues of analysis were combined and tested, that the average error amounted in one set of tliirty determinations to eight per cent, and in an- other series of twenty-six to nine per cent, of the total. With so large a margin of error, the application of the mean correction to in- dividual determinations, as well as to the determinations of a scries of twenty-one, the residues of which were not available for ex- amination, is fraught with loo much uncer- tainty. The diflfercnce, for example, between the corrections of eight ptft cent and nine per cent, would amount to nearly three times the ilitfei-encc which Professor Dittmar finds be- tween surface and bottom waters as regards their contents of lime. Fortunately, Professor Dittmar's interesting conclusion concerning the distribution of linie in ocean-water does not rest upon the individual determinations alone, but depends uijon his results with the mixtures of 'surface,' 'intermediate,' and 'deep-sea' waters, which allowed him ten times the mate- rial for an analysis which he had previously employed, and permitted the adoption of proper precautions.

Professor Dittmar's re|}ort closes with some very pertinent suggestions as to future work.

Pnil ii. contains Mr. ■). Y. Buchanan's record of something like fiAeen hundi-ed hydrometric determinations of the s}>eciQc gravity of waters from various parts and different depths of the ocean, and several jtlates illustrating the varia- tion of density ovei" the surface and in deptli. It appears that the waters of the ot>en ocean vary in density between the limits l-037«ll and 1.02400, pure water at i" C. being taken as the standard.

In part iii. StaH'-Conimaiider Tizard tabu- lates the deep-sea temperatures, and shows, by the method of co-ordinatea, the manner in which temperature varies with depth for ejicli station of observation. Tables summarizing the observations, grouping and averaging them hy localities, arc ap|>endcd.

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