Hardman — Zinc for Magnesium in Minerals. 535 
ing zinc in it, thus confirming my former analysis. It may be well to 
give the details of the examination. 
Basalt, No. 2. — The specimen was taken from the heart of a quarry 
by the road-side, in Curglasson, being more than a mile north of the 
spot where the basalt No. 1 came from. The rock was carefully exa- 
mined in the wet way for the heavy metals, &c., precipitable from an 
acid solution by sulphuretted hydrogen. Iron and alumina were pre- 
cipitated, and the filtrate then examined, much pains being taken to 
guard against error. On the addition of ammonium sulphide, a distinct 
white precipitate appeared. As it was possible that a little lime was 
also brought down, the precipitate was filtered ofi", redissolved in hydro- 
chloric acid, and reprecipitated. (a) It was again dissolved, the solu- 
tion evaporated to dryness, and ignited to drive off ammoniacal salts. 
A small portion of the residue — which was deliquescent — mixed with 
carbonate of soda, and exposed before the blowpipe on charcoal, gave 
the usual zinc oxide incrustation, which, treated with nitrate of cobalt, 
gave a vivid green. The fused bead and support, being levigated with 
water in an agate mortar, gave numerous spangles of white metal ; and 
these, when treated with a drop of water slightly acidulated with hy- 
drochloric acid, dissolved quickly with evolution of hydrogen. As the 
solution {a) could only contain zinc, with a trace of ferrous iron, and 
lime, this experiment was conclusive. 
The above results were obtained with portions of the rock treated 
in the following different ways. 
(1) The powdered rock was fused with carbonate of soda. 
(2) ,, ,, boiled in strong hydrochloric acid. 
(3) ,, boiled in nitro-hydrochloric acid. 
It is somewhat remarkable that only a trace of titanium was ob- 
served in this specimen. 
But, previous to making this analysis, I had come to the con- 
clusion that there was good reason to suspect the frequent occurrence 
of zinc in igneous as well as aqueous rocks, on the following considera- 
tion s."^' 
Zinc is very closely allied to magnesium in characteristics and be- 
haviour. In many points the resemblance is very strong,! in the me- 
tallic state as well as in combination with other elements. The salts 
of both have a similar composition ; and they, as well as the respective 
natural compounds, or minerals, are isomorphous.;]: Consequently, fol- 
lowing the law of isomorphism, the metals should be mutually replace- 
able, and wherever the one is found in any quantity, we should expect 
to find the other encroaching upon it, — ^judging by analogy of what 
* I have already pointed out that zinc minerals have been known to exist in igneous 
and metamorphic rocks. See paper already cited. 
t Fownes' Manual, of Chemistry, 10th edition, pp. 293 and 393. Also, Galloway's 
Qualitative Analysis, 5th ed., p. 49. 
X Supra cit. Also, Dana's Manual of Mineralogy, p. 74. 
