Or SEA-WATER IN THE DIFFERENT PARTS OF THE OCEAN. 
215 
water is evaporated to dryness, dissolved in water, and washed until all sulphate of lime 
is removed. This remainder contains silica, phosphate of lime, carbonate of lime, 
sulphate of baryta and strontia, oxide of iron, and probably borate of magnesia or 
lime, and is in my memorandum of the analysis mentioned under one head, with the 
designation Silica, &c. In those cases where this small remainder was not deter- 
mined, it was calculated proportionally to the quantity of chlorine. Thus, for instance, 
water taken in 44° 33' N. lat. and 42° 54' W. long, contained, in 1000 parts, chlorine 
18-842, and silica , &c. 0-069. In water taken in 47° 50' N. lat. and 33° 50' W. long., 
the quantity of chlorine was found to be IT 740, and silica is, according to the former 
proportion, calculated as 0 - 072. In this case the silica, &c. was yyj of the quantity of 
the chlorine, and in general it is less than yyy ; thus the possible error is utterly un- 
important. 
I rejected a method often used, which consists in evaporating sea- water to dryness, 
because it is inaccurate, and the result depends partly upon trifling circumstances. If 
evaporated by steam of 100° C. there will remain a very notable quantity of water, 
which quantity can only be ascertained with great difficulty. If it is dried at a higher 
temperature, muriatic acid from the chloride of magnesium will be driven out together 
with the water. I preferred thus, as I have already mentioned, to determine the quan- 
tity of the five above-named substances, to ascertain under one head all the small quan- 
tities of the different substances that remain insoluble in water, such as silica, phosphate 
of lime, &c., and to calculate the soda. At first I tried to separate the quantity of all 
the different substances in one portion of sea-water, but soon found that this method 
was neither so exact nor so easy as that which I shall now explain. 
1. Of one portion of 1000 grains, I separated the chlorine by nitrate of oxide of 
silver after I had poured a few drops of nitric acid into the water. In those cases 
where the water had fermented, I allowed it to stand in an open glass jar, in a warm 
place, until all smell of sulphuretted hydrogen had disappeared. To try how exact a 
result this method could give, I took a larger portion of sea-water, and weighed three 
different portions, each of 3000 grains, and precipitated the chlorine. The result was — 
Chloride of silver. 
145-451 
145-544 
145-642 
Mean . . 145-541 
The greatest difference is 
— 0-090 = 0-022 chlorine. 
-{-0-083=0-020 chlorine. 
These small differences are probably due to the small irregularities occasioned by the 
evaporation of very small quantities of water during weighing. The dried chloride of 
silver was as much as possible removed from the filter, melted in a porcelain crucible, 
