£5$ ■ ARSENIATED COPPER. 



Reafonsfor fhould be 47° 4' and 132° 56': now although from its minute-. 



forming a fifth j^^(^ ([^g rhomboid which exifts in this fpecies is not meafur- 

 able b}' inftruments, yel I can affirm with certainty that it is 

 much more acute than either of the two which this fuppofition 

 gives rife to. 



It is very true. Sir, (hat fince my memoir on the arfeniated 

 copper was printed, I have thought it right to feparate the 

 fpecies defcribed in it, and to make a fifth of one of the fub- 

 ftances included among them ; a fubftance which is entirely 

 different from the others in its exterior characters, and feems 

 to l6ad naturally to a belief that water muft be a principal in 

 the number of its component parts: but you are in an error 

 ■with refped to which of thefe fubftances I believe to be reallj 

 of a different nature from the others. In my firft work on the 

 arfeniated copper, I found it neceflary to make feveral fubdi- 

 vifions or varieties in the fourth fpecies: of thefe, the three 

 firft are the determinate capillary, the indeterminate capillary, 

 and that which is folid at one of its extremities, and divided 

 into very delicate fibres at the other. You feem to believe 

 that I comprehend thefe three varieties in the new fpecies 

 which I have been led to confider as an hidro-arfeniale. This 

 opinion would indeed be, as you very juftly obferve, com- 

 pletely contradictory of every thing which I have faid on thefe 

 varieties, in the delcription I have given of them, and I have 

 no doubt, muft have aftoiiifhed you. The only fpecies of arfe- 

 niated copper to which this opinion is direded, is that which 

 includes the two varieties ^o which I have given the names of 

 hematiform and amiantiform: they are very certainly the fame, 

 with this difference, that one is the produdl of the deconipofi- 

 tion of the other. 



This arfeniated copper, when it is unmixed, forms verj 

 compact mamellae, but flriated from the centre to the circum- 

 ference, and very often alfo forming different concentric lay- 

 ers: their colour is brown, ibmetimes with a very flight tinge 

 of green. This fubftance, in itsafpeCt, greatly refembles the 

 hematiform oxide of tin, which, in Cornwall, bears (lie name 

 of wood-iin; this has caufed the miners of the fame country tQ 

 give the name of wood-copper to this fpecies of arfeniated cop- 

 per. Its hardnefs, notwilliftanding its fibrous texture, is fuffi- 

 ciently great to fcratch fluated lime with facility. Its fpecific 

 gravity is from 4100 to 4200, 



This 



