a

luted into the bottle; perhaps putty is the best lute. The jar is
filled with cold water as a refrigerator ; but the principal agent in
condensing the vapour is a glass syphon (and so efficient is it, that
the condensed vapour falls guttatim into the receiver). It is placed
so as to convey cold water on to the tube which connects the retort
with the receiver, and this, trickling along it, is received by a large
bason, in which the jar and bottle stand. The tube may be luted
to flask and bottle with a stiff dough of flour and water. If the
lute is not carefully, and in sufficient quantity, applied around the
tube where it passes into the cork of the receiver, the water from
the syphon will wash it away, and into the receiver, making the
liquid cloudy, and oblige you to repeat the process. The longer
the tube is to convey the vapour, and the larger its calibre, the
better it is for your purpose. The calibre of the syphon may be
between a twelfth and a sixteenth of an inch in diameter. These
tubes may be bent in any form, with the assistance of a lamp and
blow-pipe, or a blacksmith's fire. Fearful that my description of
the still which I have been in the habit of using is not sufficiently
clear to enable any body to construct one by it, I have subjoined
a rough sketch of it as it appears when in use. The readiness with
which its materials may be had, the case with which it may be
constructed, and the convenience of such a simple apparatus to the
juvenile experimentalist, are things which I hope will in some
measure repay you for giving the above tedious description, and the
following sketch, a place, which might have been occupied by
something of more importance.
I remain, Sir, yours most respectfully,

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ARTICLE VI.
Reply to Mr. Phillips's Animadversions. By Mr. Hume.

(To Dr. Thomson.)

SIR,

When your correspondent, Mr. Phillips, shall have finished his consultation with Klaproth's Essays he will find me ready to proceed in my reply. Mr. Phillips has practised the art of garbling most dexterously in his last letter to you, it is therefore incumbent on him, in order to satisfy your readers at least, that he turn once more to the Analytical Essays, and read and explain many passages which are more immediately connected with the subject.

If Mr. Phillips be unwilling to perform the task, or ashamed to admit the truth, I shall mention a few of the items to which I refer, as proofs that Mr. Klaproth never applied nitrate of silver as a test for arsenic, and that he never, on any occasion, combined it with the oxide of arsenic, where alone it is so eminently useful; for I never heard of a single instance where the acid of arsenic had been exhibited as a poison from sinister motives. But I shall not take up your time and space further than to offer the following references to Mr. Klaproth's work.

Vol. i. p. 566. " Both the solutions of the arsenical acide in water showed exactly the same appearances which are exhibited by any other aqueous solution of arsenic.” Here is an example, where Mr. Phillips must acknowledge there can be no quibbling about the author's acquaintance with the superior efficacy of silver

, for none was used. Mr. Klaproth then proceeds. “By combination with lime-water, they (the two solutions) yielded arseniate of lime : with sulphuret of ammonia, yellow sulphuret of arsenic (orpiment); and the green pigment of Scheele, with ammoniacal oxide of copper."

If the English translation here be correct, I may remark, that arseniate of lime and the green pigment of Scheele are incompatible products from a solution of white oxide of arsenic in water; an arseniate of lime must require the acid of arsenic, and Scheele's precipitate certainly is composed with copper and the white oxide or arsenious acid.*

In every case where great exactness was required to detect and appreciate the quantity of arsenic, I do not perceive that Klaproth ever applied silver as a test. Thus, p. 140, vol. i. no silver test was used, although at p. 142, "a weak arsenical smell was perceived." He speaks of “ a slight trace of arsenic;" and some of it combined with the copper, and some with the iron.” Page 158. “ The muriate of silver emitted some arsenical vapours." Page 160. “ It is then evident that this ore consists of silver, iron, arsenic, and antimony." In the same place he notices arseniated iron.” Page 526. " A grey-yellow sublimate" and "a faint odour of

The English translation is inaccurate. The words trsed by Klaproth are arsenikalische kalkerde.-T,

a

66

66

arsenic was perceived;" yet this article is not included in the list of component parts, Page 548. The solution of variegated copper-ore in nitric acid " was tried by the proper re-agents for silver, lead, zinc, arsenic, &c." Here I am anxious to know what reagent or test Mr. Klaproth took for the arsenic, for, a more suitable and altogether palpable case for exercising the silver test does not occur in either volumę. Page 567. “ One grain of sublimed arsenic” is mentioned; “the arsenie escaped in vapours;"_" the cobalt (after calcination with charcoal) was not yet entirely deprived of all portion of arsenic.” In this case, I must observe, arsenic seems to have been deposited in place of being dissolved in the nitric acid. Indeed the whole of this essay, the analysis of the white cobalt-ore, offers many opportunities which admit of the silver test; yet it was never employed, certainly from no other cause than that the author was not aware of the value of the silver as a test, and this appears so evident through the whole of the two volumes as to admit of no contradiction,

In the second volume, page 150, the nitric acid is used to dissolve the olive copper-ore, and the acetate of lead is preferred to collect and separate the whole of the arsenic acid; and this precedes the next step the author takes, which Mr. Phillips, to serve his own purposes, has separated from the whole process of Mr. Klaproth, viz. merely to regenerate what the author supposed to be the native compound, the arsenjate of silver, described in the first volume, page 125: and this was evidently done to prove that the arseniate of lead contained no sulphate of lead, and that the arsenic found in the ore is in the state of an acid. I need not say that such conclusion must be very uncertain in all cases where an ore has been subjected to the action of nitric acid. At page 153, the author states that .“ not only the crude ore itself, but also the precipitate obtained from its nitric solution by means of acetated lead, when reduced by the blow-pipe upon charcoal, give out a vapour, which, by its garlic smell, sufficiently shows to be arsex nical :" query, the metal or oxide of arsenic? The last example which Mr. Klaproth gives us in his very excellent and most valuable essays, in which the arsenic is found, is in the pharmacolile. Here it will be seen that, after all the author's experience, including that analysis quoted by Mr. Phillips, he fixes upon the acetate of lead alone for detecting, separating, and ascertaining the arsenic acid; not a word, or the slightest allusion to a silver test; nor ia there a single syllable, or the most trifling hint from Mr. Klaproth, in any part of his work, to induce an operator to prefer silver ta lead as a test for white arsenic.

It is with much diffidence and hesitation that I offer any observation on the works of such a celebrated master as Kla. proth. It appears, however, that on many occasions the true state in which the arsenic previously existed in the ore was not completely demonstrated by subsequent experiments; for, by employing nitric acid in almost every instance, the metal became acidified, and, consequently, its primitive and more

combi

a

simple form entirely changed. I have occasionally analyzed many minerals in which arsenic made a prominent ingredient, and these were first treated by the following process, which I found to be

very successful as a preliminary operation. I boiled the pulverized ore in a solution of subcarbonate of potash, and when the solution was filtrated and allowed to cool, a sufficient quantity of acetic acid was added to saturate the solution. In all these examples I never discovered any sign of arsenic acid; for, on presenting a piece of dry nitrate of silver (lunar caustic) to the surface of the solution, I invariably procured a bright yellow, and not a red or brick-coloured precipitate. This method, as far as I can learn, has not been practised by any other person, I may therefore take this occasion to claim it as peculiarly my own. I have had no oppora tunity to analyze the red arseniate of silver, or any other arseniáte, but I have little doubt that, if such a compound be submitted to the same process, the result will be equally satisfactory, and that a brickred coloured precipitate would confirm my anticipation of one component part of such a mineral substance being the acid of arsenic.

In regard to the nitrate of barytes, that its solution is immiscible with nitric acid, and that the method employed by many chemists, before my paper was published, namely, to purify the nitric acid by adding the solution of this salt, is absurd and ineffectual, I re peat, that all I have said on that subject will defy Mr. Phillips's best efforts. Dr. Duncan, jun. has read my papers, and evidently draws a very different inference from my communication, and this Mr. Pliillips may see in the “ Edinburgh niew Dispensatory;" it'therefore remains with Mr. Phillips himself to explain what M. Bouillon Lagrange and Dr. Swediaur mean by acid: nitrique. Before I close this letter, allow me to observe, that the word barytic is omitted by Mr. Phillips in the quotation from me, in one part of his last letter; and I may here add, that, to serve his own cause

, he made a material and very gross omission of this kind, in his observations respecting the compound extract of colocyntii

, in what has been termed his acute work upon the pharmacopoeia, where he confounds proof spirit with the tincture expressed from the colocynth, which must be charged with vegetable mucilage

principles, and therefore it can no longer be considered as a proof spirit.

I am truly sorry, Sir, to have occupied your Journal by such an unprofitable subject, I trust, however, that the present communication will be not altogether uninteresting to your readers. The only apology I can make is founded upon the very illiberal

, and, ! may add, unfriendly language in the latter part of Mr. Phillips's first letter, which is evidently written with a view to injure my character. I remain, Sir, your very obedient servant, Long Acre, April 12, 1815.

Jos. HOME. [The editor hopes that neither of the gentlemen concerned will continue this dispute any longer, as it is evidently fast sinking into

4

Remarks on the Phenomena of Galvanism. In the present fluctuating state of galvanic theories, when such a variety of opinions are offered for our consideration; it may fairly be concluded that every hypothesis will be noticed in proportion to its plausibility. I shall therefore endeavour to place the subject in a different point of view from any yet published; after having made a few remarks on several opinions that have been brought forward to account for the various galvanic phenomena.

When Volta offered his simple, yet ingenious, electrical theory, to illustrate the effects of the galvanic pile, or battery, it appeared tolerably satisfactory : but as galvanic facts became more numerous, and exhibited such a novelty of character and principles, the views of this eminent philosopher were too circumscribed to embrace the great number of results that were brought to light by the rapid advance of this branch of philosophy. Although the opinions of Volta were too circumscribed to keep pace with the discoveries in galvanism, still they were too ingenious to remain uspoticed, and therefore have been remodelled by several philosophers in this country, as well as in other parts of Europe. In these alterations the ideas of Volta have been generally retained, as far as respects the electrical character of the galvanic fluid; but some writers have differed from him, by supposing that the galvanic fluid is brought into action by the chemical agency of the acid, or saline solution, used in the pile or battery, and not merely by the contact of dissimilar metals, as Volta had supposed; consequently they have been obliged to ascribe different laws to this Auid from those which were maintained by that philosopher,

In pursuing the subject of galvanism, it is extremely difficult to follow the many peculiar laws of action that this electrical view of the science enjoins, and still more difficult to reconcile all the galvanic results to those principles.

To any one well acquainted with the laws of electricity, it must appear very improbable that the negative and positive, or resinous and vitreous, state of the opposite wires of a battery, on which the most interesting phenomena are said to depend, can be obtained when they are placed in a solution that is a conducting medium : and that these phenomena, which are supposed to depend contrary electrical states of the wires, should become more as the conducting power of this medium is increased; is a result that cannot be reconciled to any well known electrical principle. By considering the galvanic phenomena agreeably to the popular theories of electricity, we must infer that many results depend on laws the very reverse of simplicity; for according to Dr. Franklin's hypothesis, we must suppose when the battery is in action that there