1530 Journal of Applied Microscopy 



are now reaching a part of the periodic system containing so many rare elements 

 that a strict adherence to the order of the periodic system is no longer practi- 

 cable if the plan outlined in VII of this series of papers is followed — namely, to 

 merely discuss the tests employed for the detection of the elements most fre- 

 quently met with in ordinary analytical work. 



The remaining articles of the series will, therefore, be devoted to the common 

 metals — mercury, lead, silver, arsenic, antimony, bismuth, tin, copper, cobalt, 

 nickel, iron, manganese, chromium. Then will follow the tests for the common 

 acids, and finally tests for several of the less common acid forming elements. 



ALUMINUM. 



Reference has already been made a number of times to this element in pre- 

 vious articles, as seriously interfering with many tests ; thus, it frequently happens 

 that an indication of its presence will be obtained while engaged in testing for 

 other elements. 



The separation of aluminum from most of the other elements has been hinted 

 at in the last article (XVII). Like glucinum and zinc, its hydroxide is precipi- 

 tated by alkalies and is soluble in excess of sodium or potassium hydroxides, 

 an aluminate of the general formula A1(0M)3 being formed. In this connection 

 it should be borne in mind that aluminum phosphate may often separate in the 

 course of micro-chemical analyses when the material containing phosphates is 

 made alkaline, or when sodium phosphate is being used as a reagent. Aluminum 

 phosphate (AIPO4 • 4H0O) is soluble in potassium and sodium hydroxides, diffi- 

 cultly soluble is ammonium hydroxide, and insoluble in these hydroxides in the 

 presence of ammonium salts. Unlike the hydroxide, aluminum phosphate is 

 insoluble in acetic acid. 



The following reagents have been suggested for the micro-chemical detection 

 of aluminum : 



I. Cesium Sulphate. 

 II. Ammonium Fluoride. 



III. Primary Potassium Sulphate. 



IV. Staining Aluminum Hydroxide with Dyes. 



/. Cesium Sulphate added to solutions containing Aluminum SuIpJiate leads to 

 the formation of Cesium Almn. 



Al2(S04)3 + CS2SO4 = [AL^CSOJ;, . Cs.^S04 • 24H,0]. 



Method. — To a drop of the solution to be tested, add a drop of ammonium 

 hydroxide. Draw off or filter off the supernatant solution. Wash the precipitate 

 once with water. Then add a single drop of water and a trace of dilute sul- 

 phuric acid, only just enough to dissolve the aluminum hydroxide. Warm 

 gently ; cool, and to the drop add a fragment of the reagent. After a few 

 seconds, beautiful large crystals of cesium alum separate (Fig. To). The crystals 

 are regular octahedra, and the usual combinations of octahedron and cube, etc. 



Remarks. — Cesium chloride can be employed as reagent, providing that the 

 solution to be tested contains a little free sulphuric acid. The chloride is, how- 



