Expansion of Salt- Solutions. 387 



construct a constant-temperature bath, which removed all the 

 difficulties and inaccuracies attending the use of long tubes. 



As I wished, so far as possible, to experiment with solu- 

 tions of definite molecular composition, and at the same time 

 to avoid the multiplication of calibration and other corrections, 

 it was not possible to employ dilatometers with tubes suf- 

 ficiently large in internal diameter to permit of the introduc- 

 tion of the solution through the graduated tube. I therefore 

 modified the form of dilatometer devised by Kremers (he. cit.) } 

 so that it presented the appearance shown in PI. V. fig. 1. The 

 bulb A is furnished with a tube at either end. One of these, 

 B, is short and bent round parallel with the side of the 

 bulb ; it is about 3 millim. external and 1 millim. internal dia- 

 meter, but at the free end is thickened and narrowed to about 

 0*2 millim. A shoulder is formed about 20 millim. from the 

 free end, by which the closing apparatus is attached. The 

 measuring-tube, C, is about 700 millim. long, and is divided 

 into millimetres from —10 millim. to 600 millim. The gra- 

 duated tubes were obtained from Geissler, of Bonn, and after 

 calibration were sealed on to bulbs of suitable capacity. 

 The dilatometer is filled through the short tube, the end of 

 which is flat, and is closed by an indiarubber pad screwed 

 down by the clamp shown in fig. 2. 



The calibration of the tubes was performed as follows: — 

 A short thread of mercury was passed through the tube 

 and measured at every 20 millim. It was found that the 

 bore was extremely uniform in all the tubes, no abrupt change 

 being perceptible. As the tubes were so long and so uniform, it 

 was considered unnecessary to do more than calibrate them 

 for more than every 100 millim. Thus, in the case of one 

 of the dilatometers Dv, a thread of mercury had the following 

 lengths at various parts of the tube : — 



At millim. length was 110 millim. 



100 



)9 



» 



111 



V 



200 



1) 



?? 



111 



yy 



300 



?) 



» 



111 



?? 



400 



?) 



J> 



111-5 



V 



500 



JJ 



)1 



110 



i) 



Mean value 110*7. 



The mean value in grammes of mercury of each millimetre 

 was obtained by weighing the mercury required to fill nearly 

 the whole of the graduated part of the tube. In the case 

 above 594 millim. contained 2'723 grm. mercury, or 1 millim. 

 contained 0*00459 grm. 



2 D2 



