the Arseniates of Copper, and of Iron. 197 
that metal contained in the ore was obtained, by boiling the 
solution with pot-ash or soda.* 
* By potash and soda, I mean those alkalis pure, obtained according to the method 
prescribed by Berthollet. I know of no other. It is not, that I have any pre- 
dilection for those identical terms ; yet, whatever melioration subsequent improve- 
ment may introduce in particular cases, if principles are to be adopted, they 
should, in general, be strictly adhered to. I^ut it must be a violation of them, to 
apply a word, appropriated by common consent to design a pure, and as yet a simple 
substance, to such heterogeneous mixtures as lapis causticus, carbonates of pot- 
ash and soda, &c. It is indeed much to be desired, that the epithets;, caustic, pure , 
saturate, &c. should be regarded as tautology, which they really are. There is no 
potash purer than potash. When it is not pure, we should say, instead of “ I took 
so much potash,” “ I took so much of a mixture of potash, and, whatever other 
substance is mixed with it.” Thus, instead of calling lapis causticus, caustic potash, or 
potash, as is often done, we should say, “ I took so much of a mixture of potash, 
sulphate, muriate, carbonate, and sulphuret of potash ; siliceous and aluminous 
earths ; iron and manganese for such I find, by analysis, lapis causticus to be. 
To all this is added, by apothecaries, a little lime. Yet this is the substance some- 
times called potash. 
M. Lo witz’s manner does not give potash pure enough for delicate analyses of. 
stones. I have never seen any prepared by his method, in which I could not discover 
iron, silica, alumina, and carbonic acid. To the proofs given by Dr. Kennedy, 
(in his paper entituled “ A Chymical Analysis of three Species of Whinstone, and 
two of Lava, in the Edinburgh Transactions for 1799,) of the efficacy of his method, 
I propose the following objections. That chymist supersaturates by nitric acid, and 
examines by nitrates of barytes and of silver. This will be a sufficient test for sul- 
phuric and muriatic acids ; but carbonic acid may have been present before satura- 
tion. He then evaporates ; and, if all is redissolvable, concludes there is no silica 
or alumina ; but, after saturation by an acid, ammonia is a more delicate test than 
evaporation, for small portions of those earths. 
By treating Dantzic potash, or, still better, pearlash, with lime, and evaporating 
in a well-plated copper vessel, a white mass is left. This mSass, dissolved as far as it 
can be in alcohol, and the liquor distilled to dryness in a plated alembic, gives an 
alkali of a perfect whiteness. In this state, it is dangerous to touch it ; its action on 
animal matter is so sudden, and so violent. It attacks all stones with the greatest ease 
and rapidity. Dissolved in water, it makes not the least cloud in barytes water, or in 
a solution of nitrate or muriate of that earth; and may be used, as a very delicate and 
sensible reagent, to distinguish it from strontian. By saturating with an acid, and then 
