109 ' On Oxalic Acid. 



This salt combines with au excess of acid, and forms a 

 sviperoxalate, long known by the name of sail of sorrel. It 

 is very sparingly soluble in water, though more so than 

 tartar. It occurs in commerce in beautiful 4-sided prisms 

 attached to each other. The acid contained in this salt is 

 very nearly double of wliat is contained in oxalate of potash. 

 Suppose 100 parts of potash 3 if the weight of acid neces- 

 sary to convert this quantity into oxalate be x, then 2 x will 

 convert it into superoxalate. 



6. Oxalate of soda readily crystallizes. Its taste is nearly 

 the same as that of oxalate of potash. When heated, it falls 

 to powder, and loses the whole of its water of crystallization. 

 Soda is said to be capable of combining with an excess of 

 acid, and of forming a superoxalate. I have not tried the 

 experiment. 



7. Oxalate of ammonia is the most iniportant of all the 

 oxalates, being very much employed by chemists to detect 

 the presence of lime, and to separate it from solutions. It 

 crystallizes in Umg transparent prisms, rhomboidal, and 

 terminated bv dihedral summits. The lateral edges are 

 often truncated, so as to make the prism 6- or 8-sided. Some- 

 times the original faces of the prism are nearly efiaced. 



The taste of this salt is bitter and unpleasant, somewhat 

 like that of sal ammoniac. At the temperature of 60^, 1000 

 grains of water dissolve only 45 grains of this salt. Hence, 

 1000 f^rains of saturated solution of oxalate of ammonia conr 

 tain only 43*2 grains of this salt. The specific gravity of 

 this solution is 1-01S6. As it may be useful to know the 

 weight of this salt contained in solutions of different spe- 

 cific gravities, I have thought it worth while to construct 

 the following table : ■ 



8. To 



