34 6 Mr. Chenevix’s Analysis of Corundum , and of 
dissolve alumina, the second to dissolve carbonate of magnesia,} 
I effected a separation of the earths. These experiments show, 
that there is an affinity between alumina and magnesia, and a 
certain point of saturation, where the action of potash upon 
alumina is wholly counteracted by the affinity of that earth for 
magnesia. 
When a solution of potash is boiled upon a mixture of lime 
and alumina, the alumina is dissolved, together with a much 
greater portion of lime than can be attributed to the dissolving 
power of the water alone. But, if a solution of potash be boiled 
upon lime, without alumina, no more lime is taken up than 
would have been dissolved by an equal quantity of water not 
containing potash in solution ; consequently, alumina seems 
really to promote the solution of lime in potash. The affinity of 
alumina for lime, 1 had mentioned in the paper to which I 
allude ; and it has since been noticed by Mr. Vauquelin.* 
If the conclusions of Mr. Guyton had been well founded, it 
would have been chemically impossible to arrive at truth jn 
analysis. There were already real difficulties enough to be over- 
come ; and Mr. Berthollet has lately discovered some, which 
are not so easily answered as those I have just considered. The 
position of this chemist, however, has been too generally ex- 
tended by him. If the power of masses were as great as he 
represents it to be, and if it increased ad infinitum , in proportion 
to the mass, it must follow, that, with any given substance, we 
could decompose any compound, provided the mass of the 
decompounding body were sufficiently great ; but this is well 
known not to be the case. 
* Scheele was,, in fact, the first who perceived this affinity. See his Essay on Sikx s 
Clay , and Alumina . 
