38 bulletin: museum of comparative zoology. 



small stop-cock near the upper end to admit air, and another near the 

 •lower end to discharge the water. 



The apparatus proved entirely reliable, perfectly water tight, and it 

 has the great advantage that it can be made by any skilled machinist 

 at small expense. The most important precautions in its manufacture 

 are to pro\ide tight stop-cocks : and to make the diameter of the tube 

 as nearly the same as that of the latter as possible. 



The water samples were preserved in "citrate of magnesia" bottles, 

 made of lead glass by the Whitall Tatum Co., with patent stoppers 

 consisting of a porcelain disc forced by a spring against a rubber ring. 

 The joint thus formed is so nearly air tight, that the danger of evap- 

 oration is negligible. As pointed out (p. 62) tests show no appreciable 

 alteration of the samples after prolonged storage. The only drawback 

 to these bottles is that they are fragile and occasionally break sponta- 

 neously as a result of sudden change of temperature. 



Current measurements were taken with an Ekman current meter. 



Salinity Avas determined by titration with nitrate of silver, the index 

 being chromate of potassium. The burette and "Knudsen" 3-way 

 pipette were supplied by Robert Goertze of Leipzig, the standard 

 water by the International Committee for the exploration of the sea. 

 This, of course, is the method almost universally employed ; and the 

 principle on which it depends has been explained by Murray and 

 Hjort, (1912) as well as by various other writers. 



The color of the sea is usually recorded by the "Forel" scale based 

 on a combination of blue and yellow, the former being .5 gram copper- 

 sulphate + 5 cc. ammonia in 95 ce. w^ater, the latter .5 gram potassium 

 chromate in 100 cc. water. The combinations used are: — 



1 2 3 4 5 6 7 8 9 10 11 12 13 



blue 100 98 95 91 86 80 73 65 56 46 35 23 10 



yellow 2 5 9 14 20 27 35 44 54 65 77 90 



In practical use a scale consisting of a series of glass tubes- is unsatis- 

 factory because of surface reflections. But these are entirely avoided 

 if the tubes be mounted in a frame above a white mirror of porcelain 

 at 45°, being thus seen by transmitted light against a white back- 

 ground. The color of the sea water is observed by means of an ordi- 

 nary plate-glass mirror mounted at 45° at the end of a pole and held a 

 foot or two below the surface on the shady side of the ship. With this 

 device, our home waters change from apparent blue to light bottle- 

 green. 



Transparency measurements were made with the ordinary white 



