JOHAN HJORT. M.-N. Kl. 



In determining the amount of salt, I have followed the method 

 adopted by Messrs. Pettersson and Ekman in their »Outlines of the H\'dro- 

 graphy of the Skagerak and Cattegat^.« The number of Grammes CI 

 (Halogen) pr. litre at 15" (Celsius) was first discovered b_v the usual 

 titration with nitrate of silver and dichromate of potash as indicator 

 (see the Hydrographical Tables). Of this the value of »the Grammes of 

 Sea Salt pr. litre of water at 15 " Celsius« was next found by multipli- 

 cation according to the factors employed by Pettersson and Ekman. This 

 was in respect to water containing 35 per 1000 of salt, 1.807; water con- 

 taining 31 per 1000, 1.8 17; and for water containing a betwixt and between 

 amount of salt, factors were employed which were found b}- the inter- 

 polation of the mentioned two factors. Of the values thus found of 

 »Grammes of salt per litre« the value was next found of »Salt per 

 thousand« by division with the specific weight of the sample. In carry- 

 ing out this, 10 samples were accurately examined in respect to their 

 chlorine contents and specific weight ( "specmc'l'efght^atT" ) (determined by 

 weighing with Sprengels pycnometer). After this a curve was drawn 

 with the amount discovered of chlorine contents as abscissae, and the cor- 

 responding specific weight as ordinates, and from the curve the specific 

 weight of all the other water samples in respect to the corresponding 

 chlorine contents was found. This was then used in the division of the 

 discovered value of »Grammes of salt per litre«. The value thus found 

 »Salt per 1000« (see the Hydrographical Tables) is therefore emplo\'ed 

 everj'-where throughout this work as the expression for the amount of 

 salt in the water, both in the letter press as well as in the accompanying 

 plates. As regards these the reader is referred to Chap. II. 



The Depth Charts I to V, ha^-e been drawn and lithographed from my 

 designs at the Geographical Surveying Institution, which, with the greatest 

 obligingness, has given me its assistance. As a basis for the charts the 

 Survey's hydrographical maps have been employed. 



As before mentioned, the surface charts A to E have been prepared 

 by Professor Pettersson. 



Numbers of gentlemen have assisted me during my labours. Profes- 

 sor Pettersson, Stockholm; Professors H. Mohn and G. O. Sars have on 

 numerous occasions yielded me their assistance in planning the work. 

 Professor Sars and Mr. Gran have, as will be seen in Chap. Ill, assisted me 

 in the revision of the notes on plankton. Mr. L. Schmelk, Town 

 Analj^st, placed his laboratory at my disposal, and at the same time 

 made up all the solutions of silver. 



I have moreover, during the collection of the material, obtained as- 

 sistance from many quarters. During my voyage on board the Com- 

 manding Officer's ship »Heimdal«, all his Officers and Captain Schiott, 

 afforded me, in my work, the greatest support. The Inspectors of the 



1 O. Petterson and G, Ekman. Outlines of the Hj-drography of the Skagerak and Catte- 

 g-at. K. Sv. Akad. Handl. Vol. XXIV, No. 11, Stockholm 1891. See pages 21 — 23. 



