t>f Copper and of Iron. 215 



and amounted to 15,5. Its other proportions I found, by 

 further analyfis, to be ^,5 of phofphoric acid, and ^t),^ of 

 oxide of copper. It is not, however, to be concluded from 

 this, that there arc really 15,5 of water of cryftaHization, in 

 blueifh green phofphate of copper. Wc mull rccolleft that 

 it is a phofphate of hydrate of copper, and that 49,5 of o.xide 

 demand 12 of water to exift in that llale : 3.5 tlierefore are 

 the amount of the water of cryfiallizatlon ; and its order of 

 imion may, with more propriety, be thus Hated : 



Water° ^"^j'^'" ^'^'"^ j forming hydrate of copper - 61,5 



Phofphoric acid - - - - S5 



Water of cryftaHization - - - 3,5 



J 00,0 

 And this is the order which fhoiild be adopted in the ftate- 

 ment of all analyfes of lalts of copper. 



I could eafily produce, by the fame method, a pale green, 

 or a brown arleniate ; and, in nature alfo, the colour of the 

 ore accurately correfponds with the proportion of water, as 

 may be feen by comparing together any of the foregoing 

 analyfes. 



Having thus convinced myfelf, by analvHs, that copper is 

 found in nature united with arfenic acid in different propor- 

 tions, I next wilhed to afcertain whether art could eftcdl 

 (imilar combinations. For this purpofe, I poured into arfe- 

 niate of ammonia, a folution of nitrate of copper, 'ihe me- 

 tallic arfeniate was immediately precipitated in cryftalline 

 grains, of a blue colour, rather more intenfe than the phof- 

 phate already mentioned; and the liqugr, which remained 

 blue, was decanted. The colour which this latter retained, 

 J imagined, was due to the prefence of a greater quantity of 

 nitrate of copper than was necelVary to precipitate, from its 

 alkaline bafis, the arfenic acid combined with the copper. After 

 a partial evaporation, I poured in alcohol ; and found, to my 

 furprile, that the coiifequence was another precipitation, 

 which was nmch increafed by allowing the liquor to remain. 

 Crvftals flill njore rich in colour than the former, and very 

 evidently rhomboidal, even to the naked eye, were gradually 

 formed. Imagining there muft be fome efltniial caufe of 

 the greater lulubility of the one than of the other, I refolved 

 to examine ihem apart. 



One hundred parts of the firft of thofe precipitates, expofed 



to a low red hi at, lofl 22. iJuiled with potafh, there remained 



unditlblved a blackifh brown powder, which, well wadied and 



dried, neighed 5c. The fupernatant liqiu^r, faturated with 



O 4 nitric 



