IN RELATION TO QUANTITATIVE CHEMICAL ANALYSIS. 
341 
The mineral. The standard solution. 
_1_ 3-7 
10,0 0 0 10 0,000 
(1) Five seconds’ exposure. (1) Five seconds’ exposure. 
The stronger. 
(2) Fifteen seconds’ exposure. (2) Fifteen seconds’ exposure. 
The least refrangible pair of lines H and K in the one photograph are of equal 
strength to those in the other. The most refrangible pair of lines are a little stronger 
in the standard solution than in the mineral. 
(3) Thirty seconds’ exposure. (3) Thirty seconds’ exposure. 
The least refrangible pair of lines in the mineral solution appear not quite so strong 
as those of the standard solution. 
(4) Five seconds’ exposure. (4) Five seconds’ exposure. 
(5) Fifteen seconds’ exposure. (5) Fifteen seconds’ exposure. 
These two series of photographs were compared, but no difference could be observed 
between them, hence it was concluded that 37 per cent, of calcium was contained in 
the mineral. 
This was not considered to be the exact proportion, because the lines had not been 
reduced sufficiently by dilution to give a good indication of the differences between 
solutions of approximately the same composition. It would not have been possible 
to carry further dilution into practice because of the complications introduced by the 
dust in the air. It is needless to say that carbon electrodes were not employed for 
the later experiment but points of gold. If we calculate the composition of the 
mineral as thus ascertained we arrive at the following numbers : — 
Per cent. Per cent. 
Mg. . 1 = MgCOg. . .3-5 
Ca. . . 37 = CaC0 3 . . . 92-5 
Total soluble carbonates 96*0 
Two analyses made in the ordinary manner by an independent analyst gave the figures 
which here follow. The separation of the magnesia was made with all possible care 
according to the directions of Fresenius/" a correction being introduced for the 
solubility of the ammonia-magnesian phosphate in the filtrate and wash-water. 
Per cent. Per cent. 
(1) Magnesium . IT7 = MgC0 3 . 4*08 
Calcium . . 36*45 = CaC0 3 . . 91*11 
Total carbonates . 95*19 
* English Edition, by J. Lloyd Bullock and Arthur Vacher, 1865, pp. 632, 273, and 167. 
