282 



Part III. — Fifteenth Annual Report 



A few extra observations of surface temperature were made, and will 

 be found under water samples 20 to 23, 44 to 48, 69 and 70, 86 to 90, 

 111 to 115, 139 to 143, 148, 164 to 169, and 174 and 175 of Table III. 



Mill's water bottle was again used for the collection of samples, and it 

 seems again necessary to emphasize the fact that this instrument, 

 although extremely useful in smooth water, was not intended by its 

 inventor to be subjected to the conditions under which the observer must, 

 unfortunately, almost always work in these seas. Some of the samples 

 brought home by the ' Research ' have obviously been collected at a 

 much less depth than was intended, through the accidental closing of the 

 bottle; these samples I have marked with an asterisk in Table III., but I 

 must confess to doubts about a considerable number of the others. 

 Fortunately, the number of samples collected at each sounding was so 

 great as to remove any serious uncertainty about the real salinities, 

 but with another type of water bottle a much smaller number of samples 

 would have amply sufficed. 



The samples were examined in the Chemical Laboratory at the 

 Museum, Oxford, partly by myself and partly by Mr H. E. W. Phillips, 

 to whom I wish to express my indebtedness, but wholly under my direct 

 supervision. They were sent to mo in bottles containing about 4 oz. 

 each ; all the important samples being supplied at least in duplicate. In 

 the case of the latter, two bottles of the same water were always examined 

 as separate samples, but no noticeable differences were observed. 



The examination was restricted in the first place to determinations of 

 salinity by chlorine estimations, controlled by density determinations 

 with Sprengel tubes. Chlorine estimations were made by the ordinary 

 chromate method, using silver nitrate solution of strength about \ 

 normal. A Geissler's 10 c.c. pipette, with fiducial mark above and below 

 the bulb, stopcock, and very fine point, was used for measuring out the 

 sea water to be titrated. This pipette was calibrated by repeated 

 weighings of its content of distilled water at temperatures from 0° C. to 

 25* C., which showed no variation exceeding 2 milligrammes, and the 

 factor for reducing its volume to exactly 10 c.c. was accordingly treated as 

 constant. The titration was performed by means of a Geissler burette, 

 with float, reading easily to 0*01 c.c. These instruments have been 

 used in estimating the chlorines of the surface samples from the North 

 Atlantic referred to above (now numbering nearly 3000), and it has been 

 found unnecessary to make the determinations in duplicate, as the burette 

 readings rarely differ by as much as 0*03 c.c. About half of the samples 

 from the ' Research ' were nevertheless titrated twice, usually with 

 different silver solutions. In dealing with the surface samples from the 

 Atlantic I hope elsewhere to discuss fully the errors of salinity determina- 

 tions based on this method, which I believe to be chiefly due to the 

 different appearance of the end reaction with sea water, and with the pure 

 sodium or potassium chloride solutions employed in ascertaining the 

 strength of the silver solutions. A personal equation of some magnitude 

 is thus introduced, which experience has shown to vary in amount from 

 time to time in the same observer, rendering control by some indepen- 

 dent method, such as the Sprengel tube determinations, essential. 



The ascertained values of [x], the chlorine per litre, have been con- 

 verted to x> the chlorine per kilogramme, and are given in column 6 of 

 Table III. Column 7 gives the salinity p as calculated from ^ by means of 

 Table XI. appended to my report on the 'Jackal' work. Column 8 

 gives the densities at 15° C. ( 4 S 15 .) ascertained by Sprengel tube, and 

 column 9 the salinities calculated from them by Table XII. of the 

 ' Jackal ' report. I may state here, pending full discussion elsewhere, 



