IOWA ACADEMY OF SCIENCES. 
131 
IV. Determinations by Miss L. B. Safely. 
1. The analysis of the substance showed its composi- 
tion as follows: 
PER CENT. 
CaCOg 41.92 
Mg C0 3 42.10 
Mg 0 = 0.81 = Mg C0 3 1.70 
Fe 2 0 3 and Alo 0 3 .... 13.62 
Si 0 2 . . . 0.88 
100.22 
2 Mg O — 0.81 per cent. 
3 Mg O = 0.78 per cent. 
4 Mg O = 0.80 per cent. 
5 Mg O = 0.72 per cent. 
6 Mg O = 1.20 per cent. 
In the last case some calcium precipitated with the 
magnesium because the calcium precipitate was not 
allowed to stand. Next used a mixture of Iceland spar 
and dolomite in which the calcium carbonate largely pre- 
dominated. 
1 Mg O = 0.47 per cent. 
2 Mg O = 0.47 per cent. 
3 Mg O = 0.47 per cent. 
4 Mg O = 0.54 per cent. 
Instead of a gram, used 0.3518 gram of the original 
dolomite, Mg 0 = 0.25 per cent. 
Again 0.2133 gram gave 0.03 per cent. 
Next a specimen of magnesite was used in which the 
amount of Ca C0 S was only 1.30 per cent. The small 
amount of Mg 0 was 0.26 per cent. The conclusion seems 
to be that the magnesium precipitated with the calcium 
varies from an almost inappreciable amount to a consider- 
able quantity. It is therefore always better to dissolve the 
unwashed precipitates of calcium and magnesium in warm 
hydrochloric acid, then to add ammonia to precipitate the 
calcium. After standing a sufficient time the calcium 
may be filtered, and the filtrate can be added to the solu- 
tion containing the main portion of the magnesium, or the 
two portions can be separately treated. 
