24 ANALYSIS AND ADULTERATIONS OP BUTTER. 



The siriking point of the weight will nearly exactly coin- 

 cide with the true fusing point, provided that the weight 

 placed on the top is not too heavy in comparison to its bulk, 

 as, for instance, a smaU piece of lead or brass would be. By 

 making use of a glass bulb containing mercury, good results 

 are obtained. 



The bulb is made by blowing a small globe on the end of a 

 piece of glass tubing of ;|-inch outside diameter, and drawing 

 it off with a tapering neck, very near the bulb. By this 

 means a pear-shaped float is obtained^ the size and shape of 

 which is given in Kg. 1. Whilst the bulb is still warm, the 

 open neck is dipped into mercury, and a smaU. quantity 

 allowed to run up into the bulb as the air contracts by 

 cooling, in the same manner as thermometers are iilled. 



Fia. 1. 



Sufficient mercury should be introduced to cause the bulb 

 to weigh 34 grammes, which is the weight of the bulb used 

 in our experiments. The bulb should displace as near as 

 possible 1 c.c. of water when immersed in a burette, its 

 specific gravity being therefore 3-4°. Absolute accuracy is 

 not necessary, since it was found that a slight difference — 

 say from 5 to 10 milligrammes — in weight, or a little variation 

 in shape, does not materially affect the results. 



