January 30, 1885/ 



SCIENCE. 



99 



parts, and that between surface and bottom 

 waters 0.0132 parts, referred to a hundred parts 

 of halogen. The fact that deeper waters do 

 contain more lime than surface-waters, Profes- 

 sor Dittmar attributes to the action of life near 

 the surface in removing lime from solution, and 

 to the tendency of bottom-waters to take it up 

 from the ocean-floor. 



As is natural, the alkalinity, too, increases 

 with depth ; and the difference between surface 

 and bottom waters in this respect corresponded 

 in Professor Dittmar's determination to 0.014 

 of lime, which is so near to the figures found in 

 the direct determination of the lime, that the 

 closeness of agreement must be accidental. 



Concerning carbonic acid in sea-w T ater, the 

 evidence goes to show, that, as a rule, it is 

 present in insufficient amount to convert to 

 bicarbonate that base which is in excess of the 

 sulphuric acid and halogen, and is free only 

 exceptionally ; that in surface-waters' it varies 

 inversely with the temperature, and for equal 

 ranges of temperature seems more abundant 

 in the waters of the Atlantic than in those of 

 the Pacific Ocean. The quantities of oxygen 

 and nitrogen absorbed b} T sea-water are func- 

 tions of the temperature. Nitrogen varies 

 within the same limits in deep and shallow 

 waters ; oxygen is generally present to a 

 smaller extent than the h}*pothesis of surface 

 absorption of atmospheric air, at the temper- 

 ature 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 often exceedingly small. 



Professor Dittmar discusses his analyses with 

 great elaboration, and devotes much space to 

 chapters upon the salinit}' and specific gravity, 

 bromine, carbonic acid, alkalinity and ab- 

 sorbed gases of ocean- water. In the analysis 

 the desirability of preciseness was constantly 

 in view. Thus, for example, much stress is 

 laid on the necessity of weighing portions for 

 analysis, as is usual with concentrated mineral 

 waters ; and, in the estimation of total halo- 

 gen by Yolhard's method, Professor Dittmar 

 secures greater accurac}' by weighing the pre- 

 cipitating solution of silver nitrate, and then 

 effecting the final titrations with centesimal so- 

 lutions of ammonium sulphocyanate and silver 

 nitrate. It is quite plain, however, and much 

 to be regretted, that the lack of water at Pro- 

 fessor Dittmar'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 magnifying of 

 inherent error a hundredfold ; and 10 cm 3 of sea- 



water, to which Professor Dittmar felt restrict- 

 ed for single determinations of total halogen, 

 is an exceedingly small portion when the result 

 is to be expressed in grams to the litre of water, 

 or in parts to the hundred grams of total 

 salts. With an adequate quantity of material 

 at hand, 40 cm 3 need not have been made to 

 serve for a determination of lime and mag- 

 nesia ; nor would such processes as the es- 

 timation of magnesia as pyrophosphate, and 

 sulphuric acid as barium sulphate, have been 

 denied ordinary care to insure the purity 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 thirty 

 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 series of twenty-one, the 

 residues of which were not available for ex- 

 amination, is fraught with too much uncer- 

 tainty. The difference, for example, between 

 the corrections of eight per cent and nine per 

 cent, w r ould amount to nearly three times the 

 difference 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 lime in ocean-water does not 

 rest upon the individual determinations alone, 

 but depends upon 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 report closes with some 

 very pertinent suggestions as to future work. 



Part ii. contains Mr. J. Y. Buchanan's record 

 of something like fifteen hundred hydrometric 

 determinations of the specific gravity of waters 

 from various parts and different depths of the 

 ocean, and several plates illustrating the varia- 

 tion of density over the surface and in depth. 

 It appears that the waters of the open ocean 

 vary in densit} T between the limits 1.02780 

 and 1.02400, pure water at 4° C. being taken 

 as the standard. 



In part iii. Staff-Commander Tizard tabu- 

 lates the deep-sea temperatures, and shows, 

 by the method of co-ordinates, the manner in 

 which temperature varies with depth for each 

 station of observation. Tables summarizing 

 the observations, grouping and averaging them 

 b} T localities, are appended. 



