From James Cumming 1821

Thursday evening

My dear Sir

I have subjoined the results of my examination of the two specimens, which you will have the goodness to insert in your Paper in what manner you may think proper. — The darker Crystals seem so decidedly Garnets that I made only a rough chemical attack upon them which is [symbol for therefore] not worth mentioning. — I regret that you have waited so long for this account

& ever | most truly yours | J. Cumming

The lighter coloured crystals, having the form of the Trapezoidal Dodecahedron, appear to be analcine with excess of Iron — They are slightly electric by friction; they scratch glass; they readily vitrify before the Blowpipe & gelatinize with acids. — The Specific Gravity of some detached Crystals was 2.293, that of a mass 2.394. — By exposure to a red heat there was a loss of 5 per cent.

The mineral was examined in the usual method by repeated digestion with muriatic acid. The residue being boiled & fused with caustic Potash. — The muriatic solution dried & heated to redness to decompose the muriates of Iron & Alumina was dissolved in water; a … of Lime was separated from the Solution, which by evaporation gave crystals of Common Salt. — Silex was obtained from the alkaline solution by muriatic acid; Alumina & Iron were precipitated by Caustic Ammonia, and Lime by the oxalate; the Iron & Alumina were separated by boiling with Caustic Potash, from which the Alumina was precipitated by Muriate of Ammonia. The results were

Silex — 49

Alumina — 17

Lime — 12

Iron — 4

Soda — 9

Water — 5

Loss — 4

= 100

The character and composition of the darker coloured crystals were are decidedly different. Their form is the Rhomboidal Dodecahedron; their hardness such that they readily scratch the former crystals; their specific gravity 3.353: they do not easily fuse before the Blowpipe, nor gelatinize in acids; in short they have all the characters of the Garnet. —

Please cite as “HENSLOW-3,” in Ɛpsilon: The Correspondence of John Stevens Henslow accessed on 27 July 2021, https://epsilon.ac.uk/view/henslow/letters/letters_3