1458 Journal of Applied Microscopy 



In the presence of zinc, only the forms of zinc oxalate are usually obtained. 



Members of the calcium group and lead are first removed with sulphuric acid 

 and a trace of alcohol. Silver with hydrochloric acid. 



In the presence of copper, aluminum, iron, manganese, chromium, nickel 

 and cobalt, the reaction with oxalic acid is not reliable and in most cases 

 worthless. 



Treated with ammonium hydroxide in the manner described under Zinc, 

 cadmium oxalate recrystallizes in the form of rods and tables. This method of 

 procedure is often of value in arriving at a decision as to the nature of a pre- 

 cipitate obtained with oxalic acid. Unfortunately, zinc prevents the formation 

 of these rod-like crystals. 



Exercises for Practice. 



Test a pure salt of Zn in dilute and in concentrated solution. Repeat the 

 experiments, substituting Cd for the Zn. 



Make a preparation of ZnCoO^ • ^H^O ; draw off the supernatant liquid ; 

 add NH^OH ; warm gently and study the preparation. Prepare slides of differ- 

 ent degrees of concentration. 



Recrystallize CdCgO^ • '^Yi<fi in the same manner as the Zn salt. 



Test mixtures of Zn and Cd. 



Recrystallize the mixed oxalates from NH^OH. 



Make mixtures of Zn and the interfering elements listed above. Treat the 

 precipitated oxalates with NH^OH. Then try Cd in the same manner. 



Try precipitating Zn with HKCgO^, K2C2O4, (NH4)2C204, etc. Then 

 try Cd in like manner. E. M. Chamot. 



Cornell University. 



Device for Leveling the Microscope. 



In examining objects in liquids on the stage of a microscope, the 



want of true level annoys by keeping up cur- 

 rents and displacing, often disastrously, the 

 object sought. 



By this simple and inexpensive device all 

 this trouble could be overcome. 



One need not even add the expense of a 

 small " spirit " level ; for a glass slip on which 

 are placed a few drops of water containing 



.r. ThreaWd hole"fo''r leyeilng screw. particles of opaque material which would 



b. Microscope pillar. , .1 . . ,• ■ -i 1 



render any tendency to current motion visible, 

 =Y= will answer the purpose. 



I : k\ Place this trial slip on the stage, and level 



by means of the three screws until no currents 



A. End view of microscope foot. . 



B. Milled hefld of leveling screw. are perceptible 



T. O. Reynolds. 



