f 



I 

















Prof. B. Silliman, Jr., on Gibhsite and Allopltane. 411 



thick, smooth except on the margins near the summit, gradually 

 acuminate, striate, the midrib vanishing about 2 in. from the base, 

 imperceptible on the upper surface. Panicle closely appressed, 



branches alternate, angled, smooth, the lowest distant, 2 hi. long, 

 becoming gradually shorter and crowded at the summit. Flow- 

 ers (5-7) subsecund upon short approximate alternate appressed 

 branchlets, pedicellate, lance-ovate, acute, pale green. Lower 

 glume lance-ovate, acute, ^-§ the length of the upper, mem- 

 branaceous, 3-nerved, the base surrounding the spikelet; upper 

 glume nearly the length of the neutral flower, 5-nerved, acute. 

 Outer palea of the neutral flower 3-nerved, the inner subequal, 

 hyaline ; both acute. Stam. 3. Herm. fl. a little shorter thftn 

 the neutral, coriaceo-membranaceous. Stamens much exserted 

 and covering the whole panicle with pale yellow anthers ; fila- 

 ments very slender, arachnoid. Stigmas large, densely plumose, 

 ochroleucous. — Fl. May — July. Society Hill, S. Car. Also, 

 Santee Canal, S. C, Mr. Ravenel, and Louisiana, Prof Car- 

 penter. Margin of ponds in water 2-4 feet deep. 



In the specimens from localities here given, I have never been 

 able to find the grain, and the flowers are very deciduous. The 

 ovary is lanceolate, acute. 



Art. XXXVIII. — On Gibbsite and Allophane, from Richmond, 



Mass. : by Prof. B. Sillimak, Jr., of Yale College. 



Gibbsite was first described by Dr. Torrey * as a terhydrate of 



alumina (Al H 3 ), and this constitution has been confirmed by 

 the analyses of Deweyf and Thomson.! More lately, how- 

 ever M. Hermann^ of St. Petersburg, has announced that the 

 constitution of Gibbsite was that of a hydrous phosphate of 



Alumina Al P-f-8 H, and that the composition assigned to Gibbs- 

 ite by Torrey, belongs only to the Hydrargillite of Rose. This 

 result is quoted by Rammelsberg|| in his third supplement, 

 who regards it as quite conformable to his own admirable re- 

 searches on the phosphates.H I was induced to repeat the analy- 



* New York Med. and Phys. Jour., No. I, p. 68. 



+ Dewey. This Jour., i ser., ii, 2 and 9 — where its close resemblance to Wavel- 

 lite was notice.!, and the minerals regarded as identical. It wm at this time un- 

 known to American mineralogists that Berzelius had but a tort time before made 

 known the real character of Wavellite m ■ phosphate and fluorid. Dr. Dewey in 

 vol. iii, p. 239, (this Journal, 1821,) proposed the name Hydrargillite as the proper 

 Me tor Gibbsite, then unknown by the latter name. 



{Outlines of Mineralogy, i, ^1 : L § Hermann, Jour. f. Pr. Chemie, xl :*2. 



Rammelsberg — Drittes supplement zu dem Handworterbuch, 184 7, p. 48. 

 f[ Rammelsberg tmtersuehang einiger naturlichen und kun^tlichen Veroindungen 

 der Phosphorsaure ; Pogg. An., B. lxiv, 407. 





