By careful 188 heating it may be made to yield the anhydrous salt.
When perfectly pure and anhydrous, it forms a white and highly crystalline mass, rapidly decomposed by air and moisture.
Nitric acid oxidises it, evolving at the same time nitric oxide; whilst sulphuric acid converts it into anhydrous sulphate.
A salt hydrate on being heated dissociates into a lower hydrate (or anhydrous salt) and water vapour.
This temperature, therefore, is the transition temperature for decahydrate and anhydrous salt.
The numbers denote grams of sodium sulphate, calculated as anhydrous salt, dissolved by 100 grams of water.
Similarly, the solubility curve of anhydrous sodium sulphate has been followed to temperatures below 32.5.
Above this temperature the anhydrous salt is the stable solid phase.
The solubility curve of the anhydrous salt does not begin until a temperature of about 260.
If the double salt is anhydrous, the point S lies at infinity, and the lines ef and gh are parallel to each other.