DETERMINATION OF THE BOILING POINT. 



769 



that represented in fig. 383. Such stands are usually sold with 

 plain and toothed rings of different sizes, so as to be used in opera- 

 tions and experiments in 

 which vessels are to be 

 heated for various pur- 

 poses. The spirit lamp 

 represented in fig. 16 

 (p. 15) is provided with a 

 support suitable for the 

 present experiment. If the 

 student cannot procure 

 one, he should clamp the 

 neck of theflask inthefork 

 of the retort-stand, pre- 

 viously placing weights 

 upon the foot of the stand 

 to prevent it from being 

 overturned by the weight 

 of the flask. Three small 

 holes are made near the 

 edge of the ring of metal, 

 the ring placed round the 

 lower part of the flask, 

 and kept in position by 

 three pieces of wire, each 

 bent at both ends, so as 

 to fit into a hole of the 

 ring at one end, while the 

 other end is suspended 

 over the edge of the 

 mouth of the flask. 



It is frequently found, 

 in testing thermometers, 

 that both fixed points are 

 higher than marked on 

 the scale. This displace- 

 ment arises from the 

 contraction of the bulb after the thermometer has been graduated 

 whereby more mercury is pushed into the stem, and its effect is 

 especially observable in thermometers which have been graduated 

 soon after being filled. If the error from this cause is not more 



3D 



FIG. 383 (an. proj. ; \ real size). 



