"To the editor of the Pharmaceutical Journal"

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To the Editor of the Pharmaceutical Journal.

Sir,--I shall be obliged if you will allow me, in reply to an observation in the last number of your journal, to state that the resemblance between the inhaler of Mr. Jeffreys, and that I have introduced for the vapour of ether, is not a coincidence, but is the result of my previous acquaintance with the former, and approval of it; and that I have never failed to mention the circumstance when saying or writing anything about the apparatus. The first notice of it in print appeared simultaneously in two medical journals, and contained the following words: "The instrument which Mr. Ferguson, of Smithfield, was making for him, was on the plan of the inhaler of Mr. Jeffreys, with some alterations and additions." (Med. Gaz. Jan. 22, p. 156, and Lancet, Jan. 23, p. 99.)

The object of the apparatus is to regulate the proportion of vapour in the air by regulating the temperature; and to effect this, I take advantage of the capacity for caloric which there is in two or three pints of water, and of the conducting power of metal of which the instrument is formed. The form I have adopted, is a matter of detail to enlarge the surface of ether exposed to the air.

The table you honoured me by publishing in the February number, is correct for ether, which is not free from alcohol, and boils at 104°. To make it correct for washed ether, which boils at 100° four degrees must be deducted; for instance, for 40° read 36°, and so on, and for washed ether deprived of its water by potash, and boiling at 98°, six [474/475] degrees must be deducted. As I have stated elsewhere, I made us in constructing that table, of the formula for the elastic force of the vapour of ether, by Dr. Ure, in his paper on Heat, in the Philosophical Transactions for 1818; having ascertained by experiments, that it could be used with correctness for that purpose.

I remain, Sir, your obedient servant,

John Snow, M.D.

54, Frith Street, Soho, March 5th, 1847.

[We regret the observation we made last month, which, from Dr. Snow's statement, appears to have been erroneous.--Ed.]