96 THE ANTARCTIC MANUAL, 
Another and very convenient form of steam generator is shown 
in Fig. 3. A is a tubulated bell-shaped vessel of tinplate, which 
passes inside the slightly larger receiver B, which holds the water to 
be boiled. The rest of the apparatus is the same as in Fig. 1. This 
form of steam generator has many advantages, and in travelling the 
lamp can be stowed inside it. 
The most important part of the apparatus is the steam tube or 
vessel C. The following are the dimensions of one which has been 
a good deal in use (Fig. 4). 
The wide part (a) is 160 mm. long, and 
41 mm. in diameter. The part (b) making connec- 
tion with the steam generator is 60 mm. long, and 
9°5 mm. wide. The upper portion (c) is 110 mm. 
long, and 15 mm. wide; and the exit tube (d) is 
50 mm. long, and 10 mm. wide. It is connected 
with the flask by means of a well-fitting cork, which 
is preferable to indiarubber as it does not adhere 
to the hot metal. From the above measurements it 
results that the internal volume of the whole tube 
is 239 c.c., and its internal surface is 291°5 sq. cm. 
The weight of the tube is 109 grms.; and if 
its specific heat be 0°2, the weight of water 
thermally equivalent to it is 21°8 grms. 
These dimensions are suitable for the thermo- 
meter which was used. The length of the tube has 
to be suited to each thermometer. For mountain 
work the thermometer should be graduated from 
85° C. to 101° C. and should be divided into tenths 
of a degree, the space between each division being 
about a millimetre, so that the length of the scale 
would be 16 cm., and that of the whole ther- 
mometer about 20 cm. It is convenient also 
to have a thermometer divided into fiftieths of a 
degree. It is essential that the thermometer be 
read entirely in the steam. If any part of the mercury extends out- 
side of the apparatus, it introduces an uncertainty which stultifies the 
use of very delicate instruments. Whatever the size of the tube 
may be, it is essential to see that all the parts are sufficiently 
wide and properly proportioned; there must be no resistance any- 
where to the passage to the steam. The lamp should be regu- 
lated to keep up a brisk flow of steam of good volume through d. 
The thermometer then finds itself immersed in saturated steam of 
