886 At one period medical men were afraid to administer any salt, of tin from an idea that arsenic was generally contained in it ; and the celebrated chemist, Margraff, affirmed, that he had found a very alarming proportion of arsenic in it. Schultz and Bayer, however, went through a most elaborate inquiry, which dissipated all apprehension. I need not point out to you of what deep importance to us it is to have ascertained this fact accurately, as so much depends in our domestic economy upon

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... e purity of this substance. The hydrochlorate of tin is the only salt that appears to have much deleterious influence on the human economy; and Orfila relates one case in his " Toxicology," which he learnt from a friend. In this it seems that diarrhoea in some, colic in others, occurred in a family in which the cook, mistaking this salt for common salt, had used it as such in preparing the dinner. There are many curious facts relating to this metal, which the alchemists called Jupiter, and its salts Jovial; but the most important one is, that Ray directed the attention of philosophers to it, when he was struck with the increase of its weight during calcination; that Boyle endeavoured to ascertain the cause of it, and that Lavoisier finally established the important doctrine, that the oxygen of the air enters into combination with metals, and thus led the way to some of the explanations of the marvellous pheaomena which chemistry now so easily and so clearly illustrates to us. The classical history of tin is peculiarly interesting, more particularly as it is connected with the earliest commerce of this country. The antiquarians have proved to us, that Phoenicia must have carried on an intercourse with this island in the earliest days of which mankind has any record. The mineralogist shows that neither in Africa or Asia, except in the East Indies, mines of tin have ever existed, and our happy island was doubtless designated In-sula3 Cassiterides, from which cassiteros, or tin, was obtained. The manner in which stream tin, the only ore of that metal, formerly wrought in Cornwall, is described by Pliny, leaves but little doubt that it was obtained from thence. Tin works are carried on there, and this is more used than that of India, although that which is purest comes from Borneo and Malacca. In the French language there are some interesting memoirs on this metal, to which I must refer you for further information; these are by Haumé, by Macquer, Pelletier, Ronelle, Bayen, and Challard ; nor have the Germans been less industrious. I am sorry to say I cannot find you even a very brief catalogue of names of English chemists, who have devoted their attention to the metals in the same complete and useful form. IT was remarked by the celebrated Lord Clarendon, " that there is no art, or science, too difficult for industry to attain. * It is that only which conducts us through any noble pursuit to a noble end. What we obtain without it is by chance, what we obtain with it is by virtue." Founded as I conceive this principle to be in truth, its fulfilment becomes only a matter of time. united to a cautious spirit of induction from facts cognisable to our senses; and if the dis. coveries of physiologists in the science of life have not been commensurate with their labours, the fact is evidently attributable to misdirected efforts to the attainment of a knowledge of the nature of a mere shadow, instead of true practical information; or, to borrow the language of Dr. Prout, " of what the vital principle is, rather than what it does.'--(On the Application of Chemistry to Physiology, &c.) But the more modern philosophers, seeing this practical error of their predecessors, in the same pursuits, have in. stituted a new order of things; and the physical phenomena of life being more within the scope of human inquiry, are now obtaining that due share of investigation, as regards details, which their importance demands, and which was formerly but too lavishly bestowed in crude conjectures on the nature of the vital essence. Life, the essence of which has been derined to be an antiseptic principle (Stahl); a a principle of self-preservation from destruction (John Hunten, Professor Bnrns); a principle analogous to electricity (Abernethy, among others) ; a chemical laboratory, in which there is carried on a multitude of chemical actions for a definitive purpose (Berzelizcs); the principles of sensibility and contractility (Bichat) the property of certain corporeal combinations, existing for a limited time, and under a determinate form, and in drawing incessantly into their composition portions of extraneous matter, whose elements they appropriate as parts of their proper structure (Cuvier) a a motion of temporary formation, in which elements remain united, which would separate did life cease, and in which elements separate without the action of caloric (Beclard); may rather, I am inclined to think, be supposed essentially to result from a normal and reciprocal action of the organic functions, and the chief of the animal functions, the brain ; of the circulation of pure oxygenated blood, and of the nervous action ; of the function of nutrition and assimilation, and of the chemical changes throughout the body, and of that action. , Without, however; subscribing altogether