42 THE BUTYRIC ACID GROUP. 



H 4 NO.C 2 O 3 -f-2HO, is obtained by neutralising oxalic acid with 

 carbonate of ammonia, and evaporating the solution; it crystallises 

 in needles, has a saline taste, effloresces on exposure to the atmo- 

 sphere, and its solubility in water is less than that of oxalic acid. 



Oxamide, C 2 H 2 NO 2 (=:H 2 N.C 2 O 2 ) is obtained either by the 

 dry distillation of oxalate of ammonia, or by the treatment of neu- 

 tral oxalate of oxide of ethyl with ammonia ; it has a crystalline 

 powdery appearance, is of a glistening white colour, has no smell or 

 taste, and dissolves very slightly in cold, but rather more freely in 

 hot water ; when strongly heated it becomes decomposed into water, 

 carbonic oxide, hydrocyanic acid, and a little urea. If a sufficient 

 quantity of water be present, a very small quantity of oxalic acid 

 can convert an infinite quantity of o'xamide into oxalate of ammonia. 



Oxamic Acid, C 4 H 2 NO 5 .HO, is an acid in which we assume 

 that oxalic acid is conjugated with oxamide (C 2 H 2 NO 2 .C 2 O 3 .HO); 

 it is produced by the dry distillation of binoxalate of ammonia; 

 it occurs as a colourless granular inodorous powder, which is not 

 readily soluble in water, and reddens litmus. When heated with 

 sulphuric acid it becomes decomposed into ammonia and oxalic 

 acid ; its salts are for the most part soluble ; at least its baryta, 

 lime, and silver salts dissolve in boiling water. 



Oxalate of Lime, CaO.C 2 O 3 , is a very important substance in 

 pathological chemistry; it occurs as a white, tasteless, and inodorous 

 powder, which, however, under the microscope, is found to exhibit 

 a distinct crystalline form. These crystals, whose crystallographic 

 relations have been carefully studied by C. Schmidt*, appear, when 

 seen with a low power, as envelope-formed, sharply defined 

 bodies; but when more highly magnified, they may easily be recog- 

 nised as obtuse square octohedra; some, however, among them, 

 are very acute. These crystals contain 1 atom of water, which they 

 lose at 180. Oxalate of lime is all but insoluble in water, and 

 it is almost proof against the action of acetic and oxalic acids ; it 

 readily dissolves, however, in the stronger mineral acids. 



Artificially prepared oxalate of lime only shows these crystals, 

 when very dilute solutions of salts of lime have been mixed with 

 diluted boiling solutions of alkaline oxalates ; under other circum- 

 stances it appears under the microscope merely in spherical or no- 

 dular masses. Crystals of oxalate of lime may be distinguished from 

 those of chloride of sodium which they much resemble in form, by 

 the easy solubility of the latter in water, and by their transparency. 

 Larger crystals of oxalate of lime sometimes occur, having some re- 



* Entwurf finer allg. Untersuchungsmethode der Safte und Excrete des thierischen 

 Organismus. Mitau u. Leipz. 1846, S. 63-65. 



