MICROCHEMIS TR Y. 59 



in concentrated hydrochloric acid and to follow the solution 

 with a polarizing microscope. The action of the acid can 

 be very much hastened by warming. 



With nitric acid calcium oxalate behaves essentially as 

 with hydrochloric acid. It is readily soluble in the former, 

 especially on warming. 



87. By sulphuric acid calcium oxalate is changed into 

 calcium sulphate (gypsum), which is little soluble in water 

 or sulphuric acid, and separates chiefly in the form of 

 needles. An immediate transformation of the calcium 

 oxalate into gypsum occurs if the sections containing it are 

 placed directly in concentrated sulphuric acid or in a mix- 

 ture of equal parts of water and concentrated sulphuric 

 acid, and heated nearly or quite to boiling. The gypsum- 

 is then formed within the same cells which formerly con- 

 tained the calcium oxalate crystals ; and each more or less, 

 opaque mass of sometimes plainly needle-shaped, sometimes 

 more granular, particles of gypsum usually possesses exactly 

 the same form as the original crystal. These crystalline 

 conglomerates glisten brightly under the polarizing micro- 

 scope. 



For distinguishing calcium oxalate from calcium sulphate^ 

 Kohl has recently (II, 194) proposed a solution of barium 

 chloride, which leaves the oxalate unchanged, while gypsum 

 crystals become covered by a finely granular layer of barium 

 sulphate. In a mixture of barium chloride and hydrochloric: 

 acid, gypsum is rapidly converted into barium sulphate,, 

 while calcium oxalate crystals disappear in the same mix: 

 ture without forming any precipitate. 



On treatment with caustic potash solution, calcium oxalate 

 at first remains unchanged ; but, as Sanio (I, 254) first 

 observed, its crystals are suddenly dissolved after some time, 

 usually after several hours, and new crystals are formed in 

 the fluid, which have the form of six-sided plates whose 

 chemical composition is not yet determined. 



88. On burning calcium oxalate crystals, which can oest 

 be done on a cover-glass laid on platinum foil, the oxalate 

 is changed first into calcium carbonate and then into cal- 



