ANALYSIS OF COMPLEX MATTER 117 



which form. This liquid is now made to evaporate and cool, 

 and the liquid again poured away from the crystals formed. By 

 repeating the process, and adding more water when necessary, 

 we shall finally obtain a number of cubic crystals distinct in 

 appearance from the others. The needle-shaped crystals, 

 being less soluble in water than the cubic ones, appear more 

 readily on a fall of temperature. 



It is difficult to separate two kinds of matter which differ 

 only slightly in solubility, and the quantities actually sepa- 

 rated may only be a small fraction of the quantities present ; 

 but a differentiation of matter has been effected. This method, 

 however, leads to no further differentiation of the two bodies 

 already separated. With regard to solubility, all the parts of 

 either body are alike. 



76. The Separation of a Complex Body into Two different 

 kinds of Matter by a Difference in their Boiling-points. A 

 mixture of alcohol and water, forming a homogeneous liquid, 

 is placed in a round-bottomed flask, with a tube fitted in the 

 cork as shown below (fig. 40). This tube is connected with a 

 condenser, which consists of a tube passing through a thicker 

 tube with two openings, by means of which a slow stream of 

 cold water may be made to condense the vapour passing 

 through the inner tube. The flask is warmed by placing it on 

 a copper water-bath. A thermometer, fixed in the cork of the 

 tube which is connected with the flask, shows the temperature 

 of the vapour coming off. 



As the fluid gradually rises in temperature, vapour will be 

 perceived to come off, and collect after condensation in a 

 vessel arranged for the purpose. The thermometer is 

 watched, and the flame regulated, so that as much as possible 

 of the vapour coming off at temperatures not exceeding 80 C. 

 may be collected. When the thermometer marks a tem- 

 perature above 80, as it will when the liquid of lower boiling- 

 point has partly passed over, the vessel for receiving the dis- 

 tillate is changed. When the temperature reaches nearly 100, 

 the distillate is again separately collected, and the distillation 

 completed. The first portion should now be freshly distilled, 

 and the vapour coming off at temperatures below 80 alone 



