345 



attained M- This apparatus, mounted for use in the laboratory 

 and fitted with pipettes of 60 cc. capacity, may be obtained 

 from Geiszler of Bonn and perhaps also from other makers. 

 The construction and use are fully described by Petterson-), 

 Sonden^) and Petterson & Palmqüist^), to whose papers I 

 must refer. 



In the figure 5 on p, 347 a modification is shown adapted for 

 use when travelling and on board ships. It differs only in 

 arrangement and points of detail from the original Petterson- 

 apparatus. Whereas in the laboratory petroleum is the most 

 suitable fluid for the index of pressure, it must be replaced on 

 board ships by the more viscous paraffine-oil, and at the same 

 time the index must be made as short as possible (about 2 mm.). 

 When these precautions are observed, and the apparatus is 

 suitably orientated with regard to the rolling or pitching of 

 the ship it will be found possible to make accurate determi- 

 nations when the movements are not too violent. 



The following general hints with regard to the performance 

 of the analyses and the possible sources of error may perhaps 

 save others some of the trouble I have myself experienced. 



The waterbath must be thoroughly mixed before each 

 reading of the burette. The best way of doing this is to force 

 a continuous stream of air-bubbles slowly through it. 



The reading of the burette is facilitated by applying a 

 simple lens mounted in a quadrangular piece of wood of suit- 

 able dimensions (see fig. 5, m). 



Ч Johansson: (Skand. Arch. Physiologie Bd. 8. 1898 p. 93) gives the 

 probable error of one analysis as 0.ooo425"/o. He has modified and 

 enlarged the apparatus and thereby diminished the probable error to 

 0.0002 °/o, but so great an accuracy is rather difficult to obtain and cannot 

 at present be considered necessary for hydrographie purposes. 



') Zeitschr. anal Chemie Bd. 2o p. 467. 



^) Ibid. Bd. 26 p. .592. Zeitschr. für Instruwenienkunde 1889 p. 472. 



^) Бег. d. deutschen ehem. Ges. 1887 p. 2129. 



