104 



Mr. G. J. Bureh. Contributions to 



[Sept 26, 



be taken if one is not enough. Four holes are drilled with a needle in 

 the positions shown. A thin piece of the best clear mica is then laid 

 on a pad of blotting paper, the piece a placed on it, and four corre- 

 sponding holes pricked through, with the needle, the piece being after- 



Fig-. 2. — <r, b, and c, full size ; cl, about twice full size. 



wards cut to the shape b. Finally, a and b are fastened together by 

 four little loops of No. 30 platinum wire, and the whole trimmed to 

 shape with the scissors. The trough is then hung by two platinum 

 chains (made of No. 30 wire with long links as shown enlarged at d 

 (fig. 2), so that the acid may not creep up them) from the hooks shown 

 in fig. 1. These hooks are best made of half-round wire, doubled like 

 a linch-pin, sliding easily but firmly in holes on each side of the 

 capillary, as in fig. 1. 



The operation of putting in a capillary is as follows : The instru- 

 ment is fixed to any convenient support by the screw M. The milled 

 head G is loosened, and the U-tube D drawn clown and turned aside. 

 The whole instrument is then tilted backwards to an angle of 45° from 

 the vertical. In this position the trough H hangs clear of the capil- 

 lary. If the capillary has been already filled and connected with the 

 pressure tube, the nuts E and F must be unscrewed far enough for the 

 tube to pass sideways into the clamps, but a new capillary may be 

 easily and safely inserted from below after merely loosening E and F. 

 It must then be filled to within 2 cm. — not nearer — of the top, with 

 recently distilled mercury from a perfectly clean pipette, connected 

 with the pressure apparatus,* and some mercury forced through. 



The screw M is then slightly loosened, and the instrument raised 

 cautiously to a nearly vertical position. The trough H is adjusted by 

 sliding the hooks from which it hangs up or down, or bending them, 

 until the capillary rests against the centre of it — the apparatus being 



* Full details of the pressure apparatus, the cleaning of the tubes, and the 

 method of drawing capillaries were given in my book. 



