228 AN ANALYSIS 
chief ingredient in sea-water, though the quantity of it may be 
affected by the changes which occur from the actions of some 
of the other salts. 
A similar conclusion is to be drawn with regard to the Mu- 
riate of Magnesia. Though the proportion of it may be affect- 
ed by the changes which occur in the analytic operations, still, 
from the quantity in which it is obtained, a considerable part 
of it must originally exist. 
The principal difficulty is with regard to the sulphate of 
magnesia, and the sulphate of soda. It has always been sup- 
posed, that sulphate of magnesia is an ingredient in sea-water, 
from its being procured by evaporation ; and it is possible that 
it may be so. But it is just as possible, @ priori, that sulphate 
of soda may be the original ingredient, and that, during the 
evaporation, the mutual action between it and muriate of mag- 
nesia, is favoured by the concentration, whence portions of 
both are decomposed, and corresponding quantities of sulphate 
of magnesia and muriate of sodaare formed. Nor is there any 
thing connected with the mere results themselves, which proves 
which of these views is just. 
If the appeal be made to experiment, it is sufficiently esta- 
blished, that sulphate of magnesia may be formed by the action 
of sulphate of soda on muriate of magnesia. When these two 
salts are boiled together in solution, a double decomposition 
takes place at least partially, and portions of sulphate of mag- 
nesia and muriate of soda are formed. On the other hand, the 
reverse combinations may also, according to circumstances, be 
established. We have seen reason to conclude, that they are 
so from the agency of alcohol; and even in an aqueous solu- 
tion, when certain proportions of the salts are used, they ap- 
pear, under some circumstances, particularly that of a low tem- 
perature, to take place toa certain extent. But still, these 
q facts 
