302 DEPARTMENT OF THE NAVAL SERVICE 



8 GEORGE V, A. 1918 



as the last trace of halide is precipitated, the potassium chromate indicates the end of 

 the reaction by forming a red precipitate with the silver nitrate. If the strength of 

 the silver nitrate has already been determined with a solution of chloride of known 

 strength, the amount of halides in the unknown solution or in the sea-water that is 

 analysed can be found by simple proportion. The solution of known strength which 

 is used in hydrography for standardizing the silver nitrate solution is the sample of 

 " normal water " which is furnished in closed glass tubes by the International Council. 

 The amount of chlorine is marked on the tube; the sample I used contained 19-386 

 parts of chlorine per thousand grams. When possible, it is well to have a few bottles 

 of the " noi-mal water " in order to occasionally titrate the silver nitrate solution ; the 

 amoimt of chlorine indicated on the tube is not absolutely reliable after the tube is 

 two-thirds empty. 



As Doctor Huntsman could only obtain, last summer, and with considerable 

 trouble, one tube of " normal water," we had to be satisfied with that. 



Here I desire to express my gratitude to the Biological Board, and especially 

 Professor Macallum, for the opportunity of taking up this study, to Dr. Huntsman, 

 the zealous and active curator of the Biological Station at St. Andrew's, who gave so 

 generously both of his time and of his experience to help me in every possible way 

 in my work, and to Sir George Garneau, professor of analytical chemistry in Laval 

 University, who helped me in the salinity determinations. 



For accurate sea-water analysis, a special burette is desirable: the ordinary 

 burette is too wide and too short for the required accuracy. The reading should be 

 certain to a hundredth part of a c.c, which is difficult with the ordinary burette. 

 Besides, the " drainage error " is greater than in the special one, the upper part of 

 which is an ungraduated bulb that terminates in a fine jet. The lower part of this 

 burette is a narrow tube graduated in hundredths of a c.c. At the present time it is 

 most difficult, not to say impossible, to obtain one of those special burettes. Dr. Hunts- 

 man was able to get one from Dr. ]\fathews, of the Plymouth Marine Biological labor- 

 atory, England, but, most unfortunately, it was broken when it reached me. Two 

 others, made to order by the Eimer and Amend Company also arrived in a broken 

 state. We hope to be fully equipped with all the special apparatus in the near future. 



DENSITY. 



The density of sea-water can be taken with a pycnometer, or else with an areo- 

 meter, at constant temperature; the second method is less accurate. But the densities, 

 though they may be accurately determined by either of the methods, do not give the 

 exact density of the water in situ, where it possessed a certain temperature and was 

 compressed by a mass of water. The density of sea-water is inversely proportionate 

 to the temperature and directly proportionate to the salinity; the lower the tempera- 

 ture and the 'higher the percentage of salts, the heavier the water. When both the 

 temperature and the salinity of a samj^le of water are known, the specific gravity may 

 easily be calculated by means of Knudsen's tables. 



When I reached the Biological Station, I began my work by making salinity deter- 

 minations of samples of water which had been collected a year before in St. Mary's 

 Bay and the Annapolis Basin. The Imperial pint bottles that contained those samples 

 were not hermetically closed; there was a deposit of salt on the covers and frequently 

 on the outside of the bottles. 



Supposing the water had evaporated, one would expect a high percentage of salts; 

 nevertheless, the results are low, and though I give them in the tables, I can, in no 

 way, guarantee their accuracy. There are other results obtained with samples taken 

 at the same sitations in September and October. 



The other samples of water were collected on the given dates at stations chosen by 

 Dr. Huntsman, where a study of the plankton is carried on along with the hydrography. 



