474 Mr Ferraboschi, A double Sulphate of Guanidine, etc. 
described, and less than the amount that would be required for 
the formation of an alum. It follows that there is, not im- 
probably, a transition temperature above which the double 
sulphate with twelve molecules of water is stable, and below 
which it cannot be obtained by simple evaporation of a solution 
of the mixed salts. 
Conversely, the hypothetical alum should have a transition 
temperature below which its formation is possible. Therefore it 
seems not unreasonable to hope that it may be possible to isolate 
it by working at a sufficiently low temperature. 
An attempt to prepare a vitriol containing guanidine and 
copper has been unsuccessful, but a double sulphate of guanidine 
and nickel has been obtained. Its description is however post- 
poned until the subject has been more thoroughly investigated. 
