342 
PROFESSOR W. 1ST. HARTLEY OH SPECTRUM PHOTOGRAPHY, ETC. 
The portion examined as stated 
above contained 
no iron or 
alumina, 
only 
insoluble residue in addition to the carbonates. The following 
analysis 
shows 
slightly different composition :— 
Per cent. 
Per cent. 
Total carbonates. 
(2) Magnesium. . 1*38 
Calcium . . 3 6'9 8 
= MgCOg. 
= CaCOo. 
4-83 ‘ 
. 92-45 
| 97-28 
Fco0 3 and AL0 3 
— 
2'24 
Insoluble residue 
— 
0-82 
Total 
100-34 
Estimations of copper .—Several estimations of copper were made with great success 
when the metal was present in not greater proportion than 5 or 6 per cent. Thus 
3‘8 per cent, and 4'2 per cent, were numbers identical with those obtained by the 
ordinary process of analysis of two specimens of pyrites. It is not, however, apparent 
that there is any advantage in estimating copper in this way, since although it may 
be sufficiently accurate and speedy, there are volumetric processes which are quite as 
satisfactory in this respect, and capable of execution with simpler apparatus. 
The spectroscope is only applicable in certain cases with advantage; when, for 
instance, it enables one to dispense with elaborate processes of separations and 
repeated weighings. I hope in a future communication to place on record the 
method of executing special assays in a perfectly satisfactory manner. 
