OF SEA-WATER IN THE DIFFERENT PARTS OF THE OCEAN. 
217 
Sulphate of lime. 
2-761 
2-753 
2- 684 
Mean . . . 2-733 
The greatest differences are — 
-0-049 = 0-020 lime. 
+ 0-028=0-012 lime. 
To find the quantity of magnesia contained in the weighed mixture of the phosphates 
of magnesia and lime, the lime, whose quantity has been determined, must, by calcu- 
lation, be converted into tribasic phosphate of lime, and deducted from the whole 
quantity of phosphates ; the other small quantities of different salts, which had been 
precipitated with the sulphate of lime, must likewise be deducted ; the remainder is 
bibasic phosphate of magnesia, from which the pure magnesia is calculated. The sea- 
water tried in this way gave, after deduction of lime, silica, &c., the following result: — 
Pure magnesia. 
3- 913 
3-970 
3-942 
Mean . . . 3-942 
The differences from the mean are — 
-0-029 
+ 0-028 
4. The determination of potash or potassium -in sea-water was tried by different me- 
thods, but gave no satisfactory results, so that I must consider the quantity of potash in 
the analyses as far less exact than any of the other substances whose quantity has been 
determined in sea-water. Happily there is so small a quantity of potash in sea-water, 
that any error in the determination of that substance has only an insensible influence 
on the whole result. For a number of the analyses I have used the following method. 
The weighed sea-water was evaporated to dryness, the dry mass again dissolved in water, 
and the undissolved residue washed with warm water until all sulphate of lime is dis- 
i solved, and the wash-water does not contain any sulphuric acid. The remaining powder 
consists of the different after-named salts and oxides insoluble in water ; it is generally 
weighed and noted under one head. 
To this solution I add so much carbonate of lime that the sulphuric acid finds lime 
enough to combine with, and as much muriatic acid as would dissolve the lime of the 
carbonate. The quantity of carbonate of lime is determined in the following way. 
The equivalent of sulphate of baryta being 1456, and that of carbonate of lime being- 
625, there will be an excess of lime if I take carbonate of lime in such a quantity that 
