SOME IMPROVED LABORATORY METHODS 



499 



heat is required, and too higli a temperature drives off uubumed 

 sulfur. 



At the end of about twenty minutes the contents of the larger 

 bottle and the test tube with rinsings should be evaporated till 

 the fumes of sulfuric acid appear. A run of even ten minutes 

 will give three to four grams of concentrated sulfuric acid. 



3. Conductivity of Electrolytes.' — It is yery desirable to have 

 every beginning student do some work on electrical conductivity 

 and electrolysis. Probably every teacher whj' bas tried to have 

 large numbers of beginners do work in this line has felt the need 

 of a suitable conductivity cell. A cell with platinum electrodes 



Fig. 169 



at the present price of platinum is practically out of the ques- 

 tion, and we are limited to carbon for this purpose. 



A conductivity cell which the crater has used with great 

 satisfaction is shown in figure 169. The only merit he claims 

 is the discovery that the spring binding post or connector of the 

 Pahnestock Electric Company, Long Island City, New York, 

 has just the right bend to clamp firmly a three-eighth carbon 

 rod. This connector and wire as shown makes a perfect union 

 of the rod and the source of electricity: The cell may be used in 

 many ways. Deliveiy tubes may be attached to the side arms 

 of the U tube and the cell used to illustrate the so-called elec- 

 trolysis of w^ater, test tubes of the same diameter serving to 

 collect the hydrogen and oxygen. Copper may be deposited on 

 the negative electrode. 



