JSl Analyjts of the Arfeniates 



of copper containing 39,7 per cent, of acid. For, if we put 

 it on the fame footing with the others, in admitting a due 

 proportion of water into its compofition, we ihall, by calcu- 

 lation, reduce it to that clafs containing 29 per cent. 



Sixthly, That in beginning with that kind which contains 

 the leaft quantity of acid, and riling progreffively to that 

 which contains the greatelt, we fliall find the order to be thus: 

 No. Vr. contains - 14 per cent. 



No. V. - - - 31 per cent. 

 Nos. I. TIT. and IV. - 29 per cent. 



No. IT. feems to be a particular fpecies. It confifts of a 

 much greater proportion of oxide, with a lefs quantity ot 

 water, (and this its external colour announces,) combined 

 with nearly the fame proportion of arfenic acid. Indeed, it 

 certain charaders did not fpeak fo ftrongly in favour of this 

 divifion, I (liould not have h.efitated to clafs it with the lalt- 

 nientioned kinds. But it is found in many ftates ; which 

 feems to indicate, that the water is by no means in the 

 fame degree of intimate combination that it is in the others j 

 and this alone may ferve to diftinguiili it to the eye of tlie 

 niineralogift. 



If, to the above natural arfeniates, is added the fecond ar- 

 tificial arfeniate, we (hall have another proportion of acid, at 

 the rate of 40 per cent. Here then we have iwo fimple fub- 

 ftances combined in four different proportions, and producing 

 feven diftincl combinations. 



But, what is not the lead to be admired, is the wonderful 

 accordance in the order which two fciences, operating witli 

 very different inftruments, have allotted to the fame fubftan«cs. 

 By that, not only the fagacity of Nature becomes very ttrik- 

 ing; but, from the acknowledged accuracy of one method of 

 invefligation, the reliance to be placed upon the other is 

 rendered more confpicuous ; and each receives, additional 

 firength and confirmation. Chemiflry has long been in the 

 habit of aiding the fcience of mineralogy, of which it laid 

 the foundation ; but it was not till lately that cryflallography 

 could form a judgment of its own, much lefs confirm the 

 truth of the fou.ce from which it fprung. 



Section II. 



Arfeniates of Iron, 



The arfeniates of iron remain now to be examined. In- 

 cluded, formerly, among arfeniates of copper, they have beca 

 feparatcd from them upon the authority of chemical analyfis. 

 For, although to recognife, by external charader and form 

 in all their modifications, fubftanccs already known, is par- 

 ticularly 



