242 Mr. Donovan on the nature and combinations 
carbonate of magnesia. The liquor after filtration was found 
to restore the original colour of reddened litmus, and to 
render green the tincture of cabbage. An acetate of lead was 
formed by boiling solution of super-acetate on carbonate of 
lead. This solution was mixed with the former, and the 
precipitate was collected by the filter. 
Notwithstanding the evident excess of magnesia existing 
in one solution, and the necessary neutrality of the other, yet 
the filtered liquor was found strongly to redden litmus paper. 
We are not to suppose that the two salts evolved a free acid 
during their mutual decomposition. As much oxide of lead 
was liberated from the acetate, as was necessary to the neu- 
trality of the acid eliminated from the compound with mag- 
nesia ; the solution would therefore have retained all its 
ingredients in a state of neutrality, except that which origi- 
nally contained an excess of magnesia. But the new salt of 
lead at the moment of its formation, was decomposed by the 
water present into a super and a sub-salt : the excess of acid 
being not only sufficient to saturate the redundant magnesia, 
but also to leave a portion free in the solution. This liquor, 
after an hour, deposited a quantity of crystalline grains, and 
after that, the acidity increased. Hence appears the reason of 
a crystallization in the original liquor : a super-salt is formed, 
which after a while deposits the neutral salt in a crystallite 
form. 
This acid appearing from what has been already stated, as 
well as from what will be hereafter detailed, to be of a 
peculiar nature, it became necessary to give it a name. After 
some consideration I bestowed on it one, which, although not 
unexceptionable, is sufficiently accordant with the general 
