198 



Appendices to Fourth Annual Report 



with the results of other observers, I have arranged in parallel columns 

 the corresponding specific gravities ^Sq and 48^5.5^. These latter being 

 calculated by means of Dittmar's tables.* 



The samples having the lowest specific gravity met with during the 

 Expedition are those taken at station 84, opposite Clachnaharry, at the 

 entrance to the Beauly Basin. Four samples were taken here at different 

 states of the tide, the influence of which is very clearly shown. The 

 specific gravities qSq ranging from 1018-385 (1016*083 4815.55) at low 

 water to 1021492 (1019-190) at high water. From this point the 

 gradually increasing salinity as we proceed down the Firth is indicated by 

 the higher specific gravity 1022*493 for station 80, and still more by the 

 specific gravity of the samples of surface water from stations 69 and 70. 

 The much higher num])ers for the samples of hottom water from station 69, 

 and even of that from station 70, somewhat higher up the firth, seems to give 

 evidence of the advance of the Salter water from the Moray Firth beneath, 

 and only very partially mixing with the fresh water finding its way down 

 from the upper reaches. The specific gravities of the samples collected 

 near the mouth of the Spey are also suggestive. At station 28, for 

 instance, the specific gravity (qSq) of the bottom water is 1028*08 — near 

 bottom 1027-21 — and at the surface as low as 1026-109, while the depth 

 at this station was in all only 4J. Several farther points of some interest 

 are suggested by the specific gravities contained in this table, but I post- 

 pone any farther discussion for the present, because whatever interest my 

 results may have there are far too few of them to be by themselves of 

 much value. 



Ratio of total Halogen to Density. 



Great additional light is often obtained by the determination of the 

 chlorine in a sample, as it frequently enables one to avoid erroneous 

 conclusions to which the unsupported specific gravity determinations may 

 seem to point. Dittmar has shown that in ocean water the ratio of the 

 chlorine, or more accurately of the total halogen calculated as chlorine 

 to the density is practically constant, and that, therefore, if the one 

 is known the other may be accurately calculated. This simply results 

 from the fact that one sample of ocean water differs from any other 

 merely by the amount of water in which the constant saline con- 

 stituents are dissolved. As a general rule no appreciable differences 

 in the relative proportions of the various saline constituents of ocean 

 water are revealed even by the most refined chemical analyses. t The 

 amount of saline matter added, even in a number of years, to the ocean is 

 almost insignificant when compared with the amount already present in it. 

 When we confine our observation, however, to the conditions obtaining in 

 localities near the mouths of rivers, the influence of the saline matters 

 carried down by the river water may become appreciable, and thus, for in- 

 stance, the ratio of total halogen to density may be altered. In such localities 

 it is not safe to rely on the specific gravity only for an insight into the 

 character of a given sample of water. Mr T. F. Barbour has determined 

 for me the total halogen contained in some of my samples by Dittmar's 

 modification of VoUhard's method, with which he was already familiar, 

 having executed most of the total halogen determinations published in the 

 * Challenger' reports. Simultaneously with the estimations of the total 

 halogen the specific gravities were redetermined, as the samples, having 

 stood some time, were appreciably altered. The results of these deter- 

 minations are given in Table IV. Without entering into any detailed 

 discussion of this table, which will be easily understood by any one 



* Challenger Reports, vol. i. t The lime varies slightly with the depth. 



