Identification of Organic Compounds. 41 



mercury in the continuous column, namely, by warming until 

 the column again reaches the reservoir, and then inverting 

 the instrument, so that part of the mercury contained in 

 the lower part of the reservoir can be made to join the 

 continuous column. By altering the amount of mercury 

 in this, it is possible, therefore, to so 

 adjust the instrument that the top 

 of the column occupies a convenient 

 position on the scale over the range 

 of temperatures at which any par- 

 ticular series of measurements are to 

 be made. It is possible to construct 

 an instrument which can be employed 

 for determinations of both boiling and 

 freezing points (ranging from below 

 zero to above 106), although the 

 range indicated on the scale does not 

 much exceed 6. It is generally, 

 however, advisable to use a single 

 thermometer over a relatively small 

 range of temperature. 



The actual apparatus for measure- 

 ment of freezing points is illustrated 

 in the accompanying illustration 

 (Fig. 16). A weighed amount of the 

 liquid is introduced into a wide- 

 mouthed test-tube A, with a side 

 tube A'. Into this is introduced the 

 Beckmann thermometer a, and a small stirrer a! (the 

 bottom of which is usually made from a fairly stout 

 piece of platinum wire bent into a loop), both of which 

 are inserted into a cork. The vessel A is itself in- 

 serted, by means of a cork at a point below the junction 

 of its side tube, into a wide tube B, which serves as an 



Fig. 16. 



