Class I.]
DB1ZE AAVAliPS—BBOCKEDON’S BLACIv-LEAD PENCILS.
atonal base of the crystal has one side larger than the rest.The dimensions of the base are 2*3G inches by 1 *97 inch,and the height of the prism 0- 105 inch. Notwithstandingthese dimensions, almost gigantic for this kind of mineral,this emerald, which is of a fine green colour, is perfectlyclear in the upper part. The lower part, which is attachedto the rock, presents many daws, probably the result of ablow by which it was detached from the veinstone.
The Duke of Devonshire is also the exhibitor of twocrystals of quartz, attached by one of the vertical faces,the crystals being each of them 2j feet high by 8 inchesin diameter. The pyramidal summits of these crystals,which rise nearly a foot above the prism, are completelytransparent, but the prisms are cloudy. These magnificentcrystals were obtained from the Alps, having been disco-vered during the formation of the read over the Simplon,in a cutting made through the old rocks.
In a series of minerals sent by the Boyal Technolo-gical Institute of Tuscany, we cannot pass over a spe-cimen of granite rock from Elba , measuring about 19inches by 13, having one side covered with magnificentcrystals of felspar, upwards of a hundred in number.These crystals, which occupy a fissure or small vein in therock, are entirely detached. They measure 2-3d inches inheight by 1*77 across between the faces g ‘: their form,extremely well defined, is a six-sided prism, composed ofthe four primitive faces M and the modifications g l ; theyare terminated by the base P, and the angle ai and a *.The enlargement of the base of the faces at and g l , givesto these crystals a peculiar arrangement observed in thelarge-grained granites of tlie centre of France , especiallyin those of La Lozere and Le Forez.
Don Francisco Ignacio Ossa, Don Miguel Gallo,and Don Ba.uon Goyenkchf., have exhibited together amagnificent specimen of native silver, weighing 154 lbs.obtained from the mine of Descubridora, near Chanar-clllo, in Chili. It was found in this mine in 1850, at adepth of 200 feet, in the vein called Augusta. The di-mensions of this specimen make it an object very remark-able in natural history ; but it is especially interesting byits structure, being formed of successive layers folded oneach other like some of the beds of the coal measures.These layers do not appear to be due to successive con-cretions, as is the case with kidney-shaped nodules ofnative arsenic.
The only other objects we shall refer to are a specimenof a lead vein from the Laxey mines, and a magnificentlump of galena from the mines of Suaiibatch, near Shrews-bury.
The fragment from Laxey represents the total thicknessof the lode, which amounts to 23^ inches, nearly. Thespecimen is about 5 feet long by .30 inches wide. It con-sists of five solid veins of galena separated by thin bandsof sulphate of barytes; and the specimen, which is one ofthe finest that we have seen, gives a complete idea of ametallic vein. The owner has presented it to the Museumof Practical Geology, where it will be of great interestas illustrating the formation of veins.
The specimen from Snailbatch mines is still more cu-rious. It is composed of an assemblage of large cubes ofgalena, measuring 3*15 inches a side, and of rhombohe-dral crystals of violet-coloured ealc spar 9-j inches long,the edges being replaced by large facets belonging to theobtuse scalenohedron : these are smooth and bright,but the faces of the vhombohedron are, on the contrary,bristled with high points consisting of the ordinarymetastatics arranged in their natural position relativelyto the axis of the rhoinbohedron, so that the faces of allthese points are parallel. This specimen, remarkable bothfor the dimensions of the cubes of galena and the crystalsof carbonate of lime, measures about 55 inches by 43Jinches, its thickness being about 14 inches.
On the Prizes Awarded and the Motives by whichthe Jury have been Influenced.
The examination of all the objects relative to mines?quarries, and metallurgical operations, and the collectionof mineral products exhibited in the Crystal Palace, wascarried on simultaneously by different members of theJury. To give greater authority to their decisions, they
obtained the assistance occasionally of persons whosespecial knowledge might assist them. This assistance theyavailed themselves of, especially with regard to thevarious specimens of iron : for the determination of which,they called in four qualified persons, whose practicalknowledge afforded every Guarantee of a just and dueappreciation. After this circumstantial examination, theJury divided the list of those whom they consider worthyof reward into three classes; the rev,ards being as fol-lows:—
1. Council Medals, for such objects as, according tothe terms originally decided ou, exhibit either novelty inthe mode of obtaining or applying raw materials andproduce, or skill and excellence in known modes of ob-taining, applying, or adapting them.
2. Prize Medals for comparative excellence in thequality obtained, combined with utility.
3. Honourable Mention of those objects which,without attaining the superiority required for the PrizeMedal, offer notwithstanding, great merit of execution orthe application of new and ingenious methods still re-quiring the sanction of long experience.
This last class has been divided into two; but it wouldbe difficult to define very accurately the difference be-tween them. To explain the difference, it may, however,be sufficient to say that the Jury have sometimes haddoubts as to whether several of those in the First List ofHonourable Mentions ought not to have been rewardedwith the Prize Medal. Difficulties of this kind havenever presented themselves in drawing the line betweenthe Honourable and Ordinary Mentions, ar.d the opinionsof the Jurors have been in all cases unanimous with re-gard to the latter.
Council Medals.
The Council Medals having been awarded in themanner above indicated, for novelty in the mode of ob-taining and applying raw materials, sanctioned by expe-rience, or for undoubted superiority in manufacture, webegin by giving seme details on the methods or kinds ofindustry that have merited them. With regard to thePrize Medals and Mentions, a general account will after-wards be given of them in the order of the respectivecountries to which they belong.
Manufacture of Black-lead Pencils by Mr. W.
Brockkdon. (Go, p. 128.)
Drawing pencils of the first quality, known in com-merce as “ Brookman's,” are made w ith small prismssawn from pure massive graphite, and placed in groovesin wood. Pieces of graphite sufficiently large to be thusused are very rare, and the mine of Borrowdale, in Cum-berland, whence they have been obtained, is almost en-tirely exhausted. Mr. Brockedon was long occupied inseeking for some method which might enable him toemploy the powder of pure graphite without cementingit by any substance, which inevitably injures the quality,lie endeavoured to render the powder coherent by sub-mittingit to enormous pressure; but the different machinesand apparatus he at first made use of for this purpose,however strongly they were made, were broken underthe pressure, and his endeavours were thus unsuccessful,until the happy idea suggested itself of operating in avacuum. But it was extremely difficult, if not impossible,to introduce under the receiver of an air-pump an appa-ratus for compressing the powder of graphite. Mr.Brockedon overcame this difficulty by an arrangement assimple as it is easily executed, for after having compactedthe graphite powder by im derate pressure, and thus re-duced it to a certain size, he enclosed it in very thinpaper, glued over the whole surface. He then piercc-d itin one place with a small round hole, permitting theescape of the air from within, when the block thus pre-pared was placed under an exhausted receiver, and theair having been removed, the orifice was closed with asmall piece of paper, and in this state it was found that itmight be left for 24 hours without injury. Being sub-mitted then to a regulated pressure once more, the dif-ferent particles became agglomerated, and a block ofartificial graphite was produced by simple pressure, as