238 



Obsewafioiis on the Temperature dinf Saliiiifv of flie Sen. 



Surface temperatures were taken with Negretti & Zambra's 

 Marine Thermometers. Temperatures below surface, with 

 Negretti & Zambra's reversing Thermometers (Scottish frame). 

 The errors of the thermometers were determined (Kew certifi- 

 cates and subsequent verifications) and were in no cases found 

 to exceed one-tenth of a degree. The thermometers at Robben 

 Island and Roman Rock supplied to the lighthouse keepers 

 were the Marine Thermometers of Negretti & Zambra, and 

 were accurate to one-tenth of a degree when sent out, though 

 no opportunity was afforded for visiting these stations sub- 

 sequently. 



The methods of analysis of sea waters were as follows : — 



The samples as received in the laboratory were examined for 

 Chlorine, Sulphuric Oxide and Specific Gravity. 



(i) Chlorine. — lo c.c. were titrated with "^^ Silver Nitrate, 

 using Chlorine free Potassium Chromate as indicator. 



(2) Sulphuric Oxide. — 10 c.c. were acidulated with Hydro- 

 chloric acid and precipitated with Barium Chloride at 100° C. 

 The precipitate was allowed t(^ stand 24 hours and was then 

 collected, washed, incinerated in muffle furnace, taking pre- 

 cautions to prevent change of Barium Sulphate, and weighed. 



(3) Specific Gravity. — Determined at 15° C in nyknometer 

 of capacity about 50 c.c. The balance used turned at yVr milli- 

 gramme. 



In all the determinations the same instruments were used and 

 the conditions of work were kept as far as possible from varia- 

 tion. All results, except those expressing the Specific Gravity, 

 are given in grains per gallon. 



