JAKOB SCHETELIG. 



far too quickly during the determination, which would therefore 

 easily be less accurate. This drawback is avoided by using a 

 bath; all that is required is that the temperature of the bath 

 shall be the same as that of the sample and the hydrometer. 

 This is easily attained by working with two cylinders and two 

 baths. While determining the specific gravity of a water-sample in 

 the one cylinder, the operator has the other standing in the other 

 bath, carefully covered to prevent evaporation. By the time the 

 first determination is finished, this second sample will have 

 assumed the temperature of the bath. The first cylinder is 

 then filled with a new sample, and placed, carefully covered, in 

 the bath, while the second is being determined, and so on. 



The glass cylinder I have used have an inside height of 

 23 cm., an inside diameter of 5*3 cm., and a capacity of about 

 500 cub. cm. 



The weights employed were made of platinum-iridium. Their 

 shape will be seen from PI. 23 fig. 4 which represents 1 gr., 

 0"2 gr., and 0"02 gr. The weights were tested at the German 

 „Reichsanstalt" at Gharlottenburg, 



The set of weights included 2 gr., 1 gr., 0"5 gr., 0*3 gr., 

 0"2 (two specimens) 0*1 gr., 0*05 gr., 0*03 gr., 0"02 gr. (two spec.) 

 O'l gr., 0-005 gr. (two spec), 0-002 gr. (two spec), and O'OOl gr. 

 (two spec). 



Weights weighing 1 mgr., on account of their minuteness, 

 and because they must be made of such thin platinum-foil, are 

 too unpractical to use, and are easily lost. But on the other 

 hand it its necessary, when the specific gravity of sea-water at 

 t° is to be determined with an accuracy of one unit in the 5th 

 decimal place, to determine the weight with an accuracy of 1 

 mgr., I would, therefore, propose that instead of the smallest 

 weights of 1 mgr. there was used, for instance, three weigbts 

 of 5 mgr., three of 3 mgr., and three of 2 mgr. By combining 

 these in various ways, it will always be possible to add or take 

 off 1 mgr., without difficulty and without loss of time. 



