308 SALTS 



be obtained by mixing together solutions of bin- 

 oxalate of potash and sulphate of magnesia in 

 the atomic proportions. No immediate precipi- 

 tate falls ; but when the liquid is concentrated, 

 crystals of birioxalate of magnesia are gradually 

 deposited. They have the form of pretty large 

 flat rectangular four-sided prisms. The taste of 

 this salt is acid, and it strongly reddens vegeta- 

 ble blues. It does not dissolve completely in 

 water ; but when digested in that liquid, a con- 

 siderable portion of the oxalic acid and some of 

 the magnesia is washed ofi\ and an insoluble ox- 

 alate of magnesia remains behind. When heated, 

 oxalic acid readily sublimes. 19*375 grains of 

 this salt were digested in water till the liquid 

 would take up no more; the undissolved oxalate 

 of magnesia weighed 5*054 grains, and contained 

 2-469 grains of oxalic acid. The dissolved por- 

 tion of the salt was mixed with muriate of lime. 

 The oxalate of lime precipitated weighed, after 

 being washed and dried in a heat of 83, 14-489 

 grains, equivalent to 6-361 grains of oxalic acid. 

 Thus the oxalic acid contained in 19*375 grains 

 of the salt, amounted to 8-83 grains, or very 

 nearly 2 atoms. 19*375 grains of the salt were 

 exposed to a strong red heat in a platinum cru- 

 cible, the magnesia remaining weighed 2-69 

 grains. But it effervesced for a little with nitric 

 acid, and therefore was not quite free from car- 



