" 4Ba On the Corundum Stone from Afta. 



particles: and in this, it differs from the fubftance of the above lump, which cuts glafs and 

 rock-cryftal with great facility. 



This lump, and the matrix of corundum, appeared to poflefs the fame properties as corim- 

 dum, when examined by the blow-pipe with the different fluxes. i 



The matrix of corundum having fometimes an appearance like adularia and feldfpar, I af-- 

 certained, by Mr. Hatchett's fcales, the fpecific gravity of adularia to be ^,558, and of feld- 

 fpar 2,555. T^^ corundum, and the lighter corundum of the lumpj cut adularia and feld- 

 fpar; the latter effervefced, and combined with foda, whicTi the former did not. 



It is, therefore, evident that the matrix of corundum, or fubfliance of the vein, is a difl;in£t 

 fubftance from adularia and feldfpar, and nearly connefted with corundum. 



The matrix, or vein, contains atfo a black fubftance like thorl, which, On clofer examination, 

 appears to be hornblende. This fubftance, Mr. Garrowliad remarked to have the appearance' 

 of charcoal ; and, on that account, he had attributed the formation of thefe ftrata to the agency 

 of fire. Other gentlemen, from the appearance of the matrix of corundum, have ftated it 

 to be a calcareous vein. 



Mr. Garrow obferved that there ran through the ftrata, in which the corundum was found, 

 veins of a fubftance like dried, pitch, apparently on their edge, which feparated like a pack 

 of cards. It is a brown micaceous fubftance, which, in drying, foliates, and fliews a certain- 

 degree of regular arrangement of the component parts ; in this cafe, the fragments of the folia 

 fubdivide with fome degree of regularity into rhombs, whofe angles are 60° and 120°: it is 

 more fmooth and lefs flexible than pure mica. 



Thefe are all the forts of corundum which I procured from India. 



I now proceed to the refult of my inquiries in China. 



I requefted Capt. Gumming, in 1786, at that time commanding t"he company's fliip, Bri- 

 tannia, to take a fpecimen of corundum to China, to afcertain its nature, and to obtain fpeci- 

 mens, if poflible, adhering to their matrix, and regularly cryftallized. On his arrival at Can- 

 ton, he collecSled the information I wifhed, with the good fenfe and zealous defire which he 

 always exerts for his friends. He afcertained that the ftone I inquired for was in common 

 ufe with the ftone-cutters ; and he brought me the ftone in its rude and in its pounded ftate, 

 taking care to feleft the moft regularly cryftallized pieces, and others adhering to the rock. 

 A ftone-cutter was fawing rock-cryftal with a hand-faw, which he alfo brought to me ; it 

 is a piece of bamboo flit, about three feet long, and i| inch broad, thickened at the handle 

 by a piece of wood, rivetted with two iron pins ; having a lump of lead tied with a thong 

 of fplit rattan, fteadying an iron pin, on which the end of a twifted iron-wire is fattened, 

 which 'being ftretched to the handle, is pafled through a hole in the bamboo with the fupcr- 

 abundant wire; a wooden peg being preffed into the hole, keeps the bow bent, and the wire 

 ftretched, and ferves to coil the fuperfluous wire, till, by fawing the cryftal, the ftretched 

 wire is worn, and requires to be renewed from the coil. The twifted wire anfwers the pur- 

 pofe of a faw, and retains the powder of corundum and water, which are ufed in this opera- 

 tion. Dr. Lind had before brought fpecimens fimilar to the above from China. 



From Sir Jofeph Banks, I obtained Dr. Lind's fpecimens, and fome in powder, which 

 Mr. Duncan, fupercargo, in China, had fent him with the Chinefe name, pou-fa. The ma- 

 trix 



