217 
the Arseniates of Copper , and of Iron. 
Fifthly, That No. I. is not to be admitted as an arseniate of 
copper containing 39,7 per cent, of acid. For, if we put it on 
the same footing with the others, in admitting a due proportion 
of water into its composition, we shall, by calculation, reduce 
it to that class containing 29 per cent. 
Sixthly, That, in beginning with that kind which contains 
the least quantity of acid, and rising progressively to that which 
contains the greatest, we shall find the order to be thus : 
No. VI. contains - - 14 per cent. 
No. V. - - - - 21 per cent. 
Nos. I. III. and IV. «* 29 per cent 
No. II. seems to be a particular species. It consists of a 
much greater proportion of oxide, with a less quantity of water, 
(and this its external colour announces,) combined with nearly 
the same proportion of arsenic acid. Indeed, if certain charac- 
ters did not speak so strongly in favour of this division, I should 
not have hesitated to class it with the last mentioned kinds. 
But it is found in many states, which seems to indicate, that the 
water is by no means in the same degree of intimate combi- 
nation that it is in the others ; and this alone may serve to 
distinguish it, to the eye of the mineralogist. 
If, to the above natural arseniates, is added the second arti- 
ficial arseniate, we shall have another proportion of acid, at the 
rate of 40 per cent. Here then we have two simple substances, 
combined in four different proportions, and producing seven 
distinct combinations. 
But, what is not the least to be admired, is the wonderful 
accordance in the order which two sciences, operating with very 
different instruments, have allotted to the same substances. By 
mdccci. F f 
