of the Fishery Board for Scotland. 



429 



Determinations of Specific Gravity. 



The specific gravity determinations made during the cruise according to 

 Mr J. Y. Buchanan's method are given in Table I., and those made sub- 

 sequently in the Chemical Laboratory of the University of Edinburgh in 

 Table IV. 



In Table I., Column XVII., gives the densities in situ; Column 

 XVIII., the densities at 15 0> 56 C. (60° F.) ; Column XIX., the specific 

 gravities at 17°-5 C. (distilled water at 17°*5 C. = 1000), and Column XX., 

 the salinities. These values were calculated from the observed specific 

 gravities by Dittmar's Tables. The values given in Columns XVII. and 

 XVIII. are directly comparable with those published in previous reports 

 by Dr H. K. Mill. Those in Column XIX. are given for comparison 

 with the specific gravities as published by the Kiel Commission. 



To those not familiar with Dittmar's Report the symbols heading these 

 columns may require some explanation. S stands for specific gravity of 

 sea water. The index to the left indicates the temperature at which 

 distilled water is taken as the standard, and the index to the right indicates 

 the temperature at which the sea water is supposed to be measured. 



Thus 4 S 15 . 56 signifies the weight of a volume of sea water measured at 

 15° - 56 C. divided by the weight of the same volume of distilled water at 

 4° C, and ^S^.g the weight of a volume of sea water measured at 17°*5 C* 

 divided by the weight of the same volume of distilled water also measured 

 at 17° *5 C. In the first case ( 4 S 15 . 56 ), as unit weight (kilogram) of 

 distilled water at 4° C. occupies unit volume (litre), the numbers given 

 under the heading 4 S 15 . 56 are the densities of the sea waters at 15°'56°. 



The values given in Table I., Columns XVII., XVIII. and XIX., agree 

 fairly well with the corresponding values given in Table IV., Columns XIV., 

 XII., and XIII. — the difference being usually less than 1 in the first place 

 of decimals (water = 1000). As will be explained later on, the values given 

 in Table IV., Column XL, giving the densities at 0° C. ( 4 S 0 ), have an alto- 

 gether higher degree of accuracy. They may be taken as correct to within 

 one in the second place of decimals. This, of course, is equally true of 

 the values given in Column VII. under the heading 0 S 0 , these being the 

 values arrived at by dividing the actually observed weights of given 

 volumes of sea water measured at 0° C. divided by the actually observed 

 weights of the same volumes of distilled water at 0° C. All these weigh- 

 ings were subjected to a correction for the displaced air, the density of 

 the air at the time of weighing being calculated from readings of the 

 barometer and wet and dry bulb thermometer. In these determinations 

 of specific gravity a modified form of Sprengel's pyknometer was used as 

 described in my former reports. The values given in Table IV., Columns 

 XIL, XIII., and XIV., are certainly more accurate than those in Columns 

 XVIL, XVIII. , and XIX. of Table I., but are necessarily less accurate than 

 those given in Columns VII. and XI. of Table IV. inasmuch as these 

 latter are independent of any assumption as to the exact amount of altera- 

 tion produced in the volume of the different sea waters by change of 

 temperature. 



Throughout the following discussion of the results arrived at, the word 

 density when unqualified is to be taken as meaning density at 15°-56 C, 

 the numbers being taken from the columns headed 4 S 15 . 56 and preferably 

 from Table IV. giving the results of the determinations made in the 

 Chemical Laboratory of the University of Edinburgh, these being the 

 more accurate. 



The facts ascertained with regard to the density of the sea water in the 

 different parts of the North Sea visited by the ' Jackal ' in September and 



