QUANTITATIVE ANALYSIS BY MEANS OF THE MICROSCOPE 219 



As small amounts as 25 to 50 milligrams may successfully be 

 used. 



For special precautions, sources of error and suggestions as 

 to the choice of solvents and standards, the student is referred 

 to the original article. 



This method of Barger's for the determination of molecular 

 weights is another example of the manifold applications of the 

 microscope. The microscopist whose laboratory is seldom 

 equipped with apparatus for the determination of molecular 

 weights by the usual methods of boiling or freezing points, or 

 by vapor densities, may nevertheless obtain sufficiently accurate 

 results for all practical purposes by the procedure outlined 

 above. 



The method is worthy of far more attention by analysts 

 than it has been given. 



